The 2017 Atlantic Hurricane Season Summary

1 12 2017

Dale C. S. Destin|

The 2017 Atlantic hurricane season came to an end yesterday but will long be remembered for the costliest and one of the most destructive on record. It was also one of the most active hurricane seasons on record, breaking or equalling several records.

Hurricanes Katia (left), Irma (middle) and Jose (right)

Hurricanes Katia (left), Irma (middle) and Jose (right)

The hyperactive season produced 17 named storms, 10 hurricanes, 6 major hurricanes and 223 Accumulated Cyclone Energy (ACE). Overall, it is the seventh most active season on record (based on ACE) dating back to 1851 and the most active since 2005.

AtlanticHUrricaneSeasonSummary

Relative to the normal season of 12 named storms, 6 hurricanes, 3 major hurricanes and 106 ACE, this season had 42% more named storms than normal, 67% more hurricanes than usual, twice the normal number of major hurricanes and over twice the normal amount of ACE.

2017HurricaneSeasonSummaryGraphic

The furious 2017 Atlantic hurricane season left in its wake cataclysmic damage and is now the costliest hurricane season on record with cost amounting to over US$367 billion. The Caribbean contribution to this total is about US$120 billion.

Relative to Antigua and Barbuda

It was the most active hurricane season for Antigua and Barbuda, based on the number and strength of hurricanes passing within 105 nm of the islands. This season marks the first time on record that three major hurricanes passed in such proximity of the country. There have been other times with three or more tropical cyclones but none with three major hurricanes.

For the first three weeks of September, we had a ominous procession of major hurricanes – Irma, Jose and Maria. Irma was the strongest, in terms of sustained winds. The current hurricane scale goes from 1 to 5; however; if there were a 6, Irma would have been a Category 6 – it was super strong with peak sustained winds of 298 km/h (185 mph).

Super-Category 5 Hurricane Irma virtually wiped out Barbuda – damaging or destroying around 90% of buildings. Meanwhile, Antigua got away almost “scot-free” with only storm-force winds causing minimal damage.

Damaged and destroyed properties in Barbuda in the wake of Irma – Sep 6, 2017

Both Antigua and Barbuda dodge the bullets from Jose and Maria. Maria also produced storm-force winds; however, Jose passed without causing any notable winds. Notwithstanding, with Jose passing three days after Irma destroying Barbuda – the whole island had to be evacuated.

The expense to Antigua and Barbuda according to the National Office of Disaster Service (NODS): about US$140 million in damage; around US$20 million in losses and a recovery cost of about US$220 million. Most of the damage took place on Barbuda, where one person died during the passage of Irma.

On average, Antigua and Barbuda gets one named storm passing within 105 nm every other year, one hurricane every three years and a major hurricane every seven years. This is the first year on record we have been affected by Category 5 hurricanes – Irma and Maria.

AntiguaHurricaneSeasonSummary

Why was the season so active?

The season was hyperactive because of warmer than normal sea surface temperatures and very friendly atmospheric conditions – deep moisture levels and below normal vertical wind shear. This was especially so from around mid-August to early September.

The absence of an El Nino and conditions trending toward a La Nina also allowed for a more active season than normal.

Did climate change play a part?

There is no scientific evidence to support the notion that climate change had anything to do with the hyperactive 2017 Atlantic hurricane season or any previous hurricane season.

This is not to say that climate will not eventually have an impact on the hurricane season in the future. According to the Intergovernmental Panel on Climate Change (IPCC), climate change will, in the future, cause an overall decrease in the number of tropical cyclones but an increase in the number of major hurricanes.

Other notable records

Irma is the strongest hurricane on record to occur in the Atlantic Ocean – outside the Caribbean Sea and the Gulf of Mexico.

Maintaining peak intensity for 37 consecutive hours, Irma is the only tropical cyclone on record worldwide to have had winds that strong for so long.

Irma tied with 1935 US Labour Day hurricane for the strongest hurricane to ever make landfall in the Atlantic Basin.

September 2017 is the most active month on record for the Atlantic

Ten hurricanes in a row form during the 2017 Atlantic hurricane season – the most consecutive hurricanes on record.

Click here for more records.

Keep following for more on the just ended hurricane season, tropical cyclones and climate change and all things weather and climate. The next hurricane season starts June 1, 2018 – six months from now, let us all be prepared. Our first forecast for the next season will be issued around April 10.

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Tropical Cyclone Size and Climate Change

21 11 2017

Dale C. S. Destin |

This is a continuation of our series – Tropical Cyclones and Climate Change – TCs (tropical depressions, tropical storms, hurricanes). In our previous blog in this series, we looked at Tropical Cyclone Rainfall Rates and Climate Change. In this blog, we will look at whether climate change is having an impact on TC size.

The soon ended 2017 Atlantic hurricane season has produced 17 named storms – five more than the average or 42% more than usual. This is still the most since 2012, when 19 formed. Meanwhile, there have been 10 hurricanes – four more than the average or 67% more than usual. This season remains tied with 2010 for the most hurricanes since 2012. The number of major hurricanes remains unchanged at six – three more than average or twice the usual amount. This is the most major hurricanes since 2005.

Have TCs size increased?

The Intergovernmental Panel on Climate Change (IPCC) is silent on this question. Further, the research on TC size has been quite few and the datasets very limited; however, the current answer is likely no based on available data.

Studies have shown that the size of TCs varies within and across ocean basins. Generally, the size of TCs increases with the increase in latitude or as you move poleward. For the Atlantic, this means that they generally increase in size as you go northward.

Hurricanes Katia (left), Irma (middle) and Jose (right)

Hurricanes Katia (left), Irma (middle) and Jose (right). All three were small hurricanes in terms of the extent of the hurricane and storm winds from their centres.

The initial size of a TC is also indicative of its eventual size when it reaches the maximum intensity. The rate of growth is largest at intensification.

There appears to be a trend toward smaller TCs in most ocean basins that they do form over; however, this trend is not deemed to be significant globally or regionally.

While there appears to be a negative trend in most ocean basins, no significant trend in size have been detected globally or regionally. However, the confidence level of this finding is considered relatively low since the dataset used is relatively short and somewhat subjectively obtained.

Will TCs increase in size in the future?

Although some studies have indicated a decrease in size, it is not clear how size will change in the future with a warming climate. The increase in intensity could be theorized to have both a positive or negative trend on size.

More intense TCs could mean higher pressure gradients due to a tightly ‘rap’ system and no change in central pressure, in that case, the trend in size could be toward smaller systems. On the other hand, if cyclones exhibit lower central pressure, then the trend in size could be toward larger systems. Much more research is needed in this area.

There are lots of talk in the press about TCs becoming larger due to climate change; however, there is no clear evidence to support this claim. There are two main scientific papers that address this matter – one found that the size is decreasing and the other said that the size will increase. However, both papers agree that no change in size has yet occurred due to climate change.

Our next blog in this series will look at the impact, if any, of climate change on tropical cyclone duration.





Tropical Cyclone Frequency and Climate Change

17 10 2017

Dale C. S. Destin |

This is a continuation of our series – Tropical Cyclones and Climate Change – (TCs; tropical depressions, tropical storms, hurricanes). In our previous blog in this series, we looked at Tropical Cyclone Intensity and Climate Change. In this blog, we will look at whether climate change is having an impact on TC frequency.

Hurricanes Katia (left), Irma (middle) and Jose (right)

Hurricanes Katia (left), Irma (middle) and Jose (right) – Sep 8, 2017

To date, the 2017 Atlantic hurricane season has produced 15 named storms – three more than the average or 25% more than usual. This has equalled the number of storms for last year. Meanwhile, there have been 10 hurricanes – four more than the average or 67% more than usual. This tied with 2010 for the most hurricanes since 2012. Further, there have been six major hurricanes – three more than average or 100% more than usual, the most since 2005.

Have TCs become more frequent?

According to the Intergovernmental Panel on Climate Change (IPCC), it is unlikely that TCs have become more frequent. Recall that the IPCC is the United Nations’ body task with assessing climate change.

Here is what the IPCC Assessment Report Five (AR5) actually says: “…recent assessments indicate that it is unlikely that annual numbers of tropical storms, hurricanes and major hurricanes counts have increased over the past 100 years in the North Atlantic basin…”. “No robust trends” exist.

So, having examined hundreds of peer-reviewed scientific research papers on the subject, the IPCC concluded that there has been change in the frequency of tropical cyclones.

One of the many papers cited by the IPCC, explains not only that there has been no change in the annual number of TCs but that there have been previous active Atlantic TC eras similar to the present. These active eras alternate with inactive eras; hence, in the not too distant future, the Atlantic will return to an inactive phase, perhaps similar to the 1970-1994 interval, when fewer storms occurred.

Further, although there has been no change in the number of  TCs over the past 100 years, research suggest that relative to about a thousand years ago, the annual number of TCs have decreased significantly. This is supported by Michael E. Mann et al., Michael J. Burn and Suzanne E. Palmer and others.

The increased greenhouse gases, the cause of climate change, substantially explain the observed SST increases over such places as the Atlantic and North West Pacific during the last 50 years. Added to this, are the apparent significant increases in TCs over this period. However, when the raw dataset is adjusted for short-lived TCs i.e. TCs lasting less than two days, a different picture emerges.

NA_TCs_Raw&Adjusted

Green-shaded curves depict global mean temperature (HadCRUT3 data set) and August–October main development region (MDR; 10° N–20° N, 80° W–20° W) SST anomalies (HadISST data set). Blue-shaded curves represent unadjusted tropical storm counts. Red-shaded curves include time-dependent adjustments for missing storms based on ship-track density. The curve labelled ‘>2-day’ depicts storms with a duration greater than 2.0 days. Orange-shaded curves depict US landfalling tropical storms and hurricanes (no adjustments). Solid black lines are five-year means (1878–2008); dashed black lines are linear trends. Vertical axis ticks represent one standard deviation. Series normalized to unit standard deviation. Only the top three series have significant linear trends (p = 0.05). Source: Knutson et al. 2010

Before the satellite era – pre-1966, a number of storms went undetected due to the fact that they never made landfall and occurred in unfrequented parts of the Atlantic Ocean by ships – the only source of TC detection over open waters before there were satellites. Thus, when the raw data is adjusted for these missing cyclones, no long-term trend is detected.

The trend in major hurricanes is not (statistically) significance. Notwithstanding, the current trend is unreliable since studies have shown that the wind speeds for TCs, over the period 1851 to 1920, were systematically underestimated, a fact supported by paleoclimatology.

To a great extent, the numbers of TCs on record, pre-1966, are there only because they made landfall. Counting landfalling TCs is not a robust method for determining overall trend; nevertheless, the method shows no trend in various regions of the world.

Will TCs become more frequent in the future?

To this question, the IPCC says no! Here are the exact words from the IPCC AR5, “…it is likely that the global frequency…of tropical cyclones will either decrease or remain essentially unchanged…. However, “substantial increases in the frequency of the most intense cyclones and it is more likely than not that this increase will be larger than 10% in some basins”.

One of the main scientific papers used by the IPCC to come to this conclusion is one done by Knutson TR, McBride JL, Chan J, et al. They say that late in this century, there will be a 6 to 34% decrease in TC frequency. However, on the other hand, the same paper projects a 2 to 11% increase in TC winds; hence, by virtue of this, predicts an increased frequency of major hurricanes being more likely than not by year 2100. Notable TC researchers Kevin J.E. Walsh, John L. McBride, Philip J. Klotzbach et al. endorsed this conclusion.

TrendOfTCs

General consensus assessment of the numerical experiments described in Supplementary Material Tables 14.SM.1 to 14.SM.4. All values represent expected percent change in the average over period 2081–2100 relative to 2000–2019, under an A1B-like scenario, based on expert judgement after subjective normalization of the model projections. Four metrics were considered: the percent change in (I) the total annual frequency of tropical storms, (II) the annual frequency of Category 4 and 5 storms, (III) the mean Lifetime Maximum Intensity (LMI; the maximum intensity achieved during a storm’s lifetime) and (IV) the precipitation rate within 200 km of storm centre at the time of LMI. For each metric plotted, the solid blue line is the best guess of the expected percent change, and the coloured bar provides the 67% (likely) confidence interval for this value (note that this interval ranges across –100% to +200% for the annual frequency of Category 4 and 5 storms in the North Atlantic). Where a metric is not plotted, there are insufficient data (denoted ‘insf.d.’) available to complete an assessment. A randomly drawn (and coloured) selection of historical storm tracks are underlain to identify regions of tropical cyclone activity. Source: IPCC AR5

One of the fallacious arguments being advanced for the increase in the frequency of TCs is increasingly warmer SSTs being caused by climate change. But quite obviously, warm SSTs are not the only parameters required for increased frequency. SSTs are very necessary but far from being sufficient for causing increased TC frequency.

A recently issued paper by Jeffrey P. Donnelly & Jonathan D. Woodruff indicates that such high SSTs as at present are not even necessary to support periods of frequent major hurricane activity. There have been eras with similar or higher number of TCs with significantly lower SSTs.

The Kevin J.E. Walsh et al. paper indicates the models used to simulate TCs, produce an increased frequency of TCs as temperature decreases and decreased frequency when temperature increases. Thus, increased SSTs do not necessarily mean increased TC frequency, by consensus, the opposite seems to be true.

Also required for increased number of TCs are conducive atmospheric conditions – unstable Atmosphere, moist middle Atmosphere and the overturning of the tropical Atmosphere caused by the Hadley cell. All three are needed for the formation of tropical disturbances – the precursors of TCs. However, fortunate for us, climate change is causing these things to go in the negative direction; hence, the projected decrease in the frequency of TCs by the end of this century.

Based on the IPCC and the vast majority of the TC researchers, TC frequency has not changed over the last century. By the preponderance of research papers, climate change has NOT caused TCs to become more frequent. However, by late this century the frequency of TCs is projected to decrease or perhaps remain unchanged relative to present. However, the number of major hurricanes is more likely than not to increase late in the current century. This is the conclusion of the IPCC AR5 – we either accept the full report or none at all. And if we accept all of it, we would not be blaming current TC and hurricane frequencies on climate change, at this time.

Our next blog in this series will look at the impact, if any, of climate change on tropical cyclone rainfall.





Tropical Cyclone Intensity and Climate Change

5 10 2017

Dale C. S. Destin|

This is a continuation of our series – Tropical Cyclones and Climate Change – TCs (tropical depressions, tropical storms and hurricanes). In this blog, we will look at whether climate change is having an impact on TC intensity/strength, especially with respect to wind speeds and provide you scientifically based answers.

As many Caribbean islands rebuild after the havoc caused by Hurricanes Irma and Maria, which killed over 185 persons and caused over US$150 billion in damage, many – including political leaders, have declared that these hurricanes were caused by climate change.

Even the United Nations (UN) Secretary-General seems to be peddling the notion that climate change caused Irma, Maria and the hyperactive 2017 Atlantic hurricane season.

But is climate change really to be blamed? Are these statements in harmony with the findings of the Intergovernmental Panel on Climate Change (IPCC)? What is the consensus of TC researchers?

The 2017 Atlantic hurricane season

Thus far, the season has produced 14 named storms, 8 of which became hurricanes and 5 major hurricanes – Category 3 and over. Of the 5 major hurricanes, 2 (Irma and Maria) became Category 5 – the highest category on the Saffir-Simpson Hurricane Wind Scale.2017 Atl Hurricane Season TracksRecord shows that Hurricane Irma was no ordinary Category 5 Hurricane. Far from it – it was more like a Super Category 5 Hurricane. If there were a Category 6 – it would have easily been so categorised.

Hurricanes Irma and Maria are among the strongest hurricanes to ever form over the Atlantic Basin. Irma had peak sustained winds of 295 km/h (185 mph), which makes her joint holder with three other hurricanes for the second strongest Atlantic hurricane on record, dating back to 1851. Only Hurricane Allen of 1980 was stronger with 305 km/h (190 mph) winds. As for Maria – her peak sustained winds of 280 km/h (175 mph) tied her with seven other hurricanes for the eighth strongest on record.

Super Category 5 Hurricane Irma on our doorsteps

Super Category 5 Hurricane Irma on our doorsteps – Sep 5, 2017

Have TCs become more intense?

According to the IPCC, “unlikely“. The IPCC is the UN international body designated to assess the science of climate change. It was set up in 1988 by World Meteorological Organization (WMO) and UN Environment Programme (UNEP) to provide policymakers with rigorous and balanced scientific information on climate change.

This is what the IPCC Assessment Report Five (AR5) – the latest report, says about the impact of climate change on TCs: “In summary…recent assessments indicate that it is unlikely that annual numbers of tropical storms, hurricanes and major hurricanes counts have increased over the past 100 years in the North Atlantic basin…”

So, based on the examination of many peer-reviewed scientific research papers, the IPCC concluded that there is no trend in the intensity of tropical cyclones – there is no robust data to support the notion that climate change has caused TCs to be “stronger and bigger” “with each passing hurricane season”.

There is, however, a line in the IPCC report that some may point to as evidence of climate change causing TCs to be stronger. It says: “Evidence, however, is for a virtually certain increase in the…intensity of the strongest tropical cyclones since the 1970s in that [North Atlantic] region.” Is this an endorsement of the view that climate chance is causing TCs to be stronger? Certainly not.

TC activity in the North Atlantic, like most places, go through phases – inactive and active periods that last for multiple of decades at a time, which are closely linked to the Atlantic Multidecadal Oscillation (AMO). Active phases are marked by above normal number and strength of TCs and the opposite for inactive phases.

3-Year-Average ACE

A plot of three-year-averaged Accumulated Cyclone Energy (ACE). It is a measure of the activity of a hurricane season based on strength, duration and the number of TCs. It shows the active and inactive phases of the Atlantic hurricane season. These phases are natural – NOT caused by human-induced climate change.

So, from the 1970s to the mid-1990s, the Atlantic went through an inactive phase, where there was a decline in the frequency and intensity of the number of TCs from the mid-1920s to 1960s – the previous active period before our current one.

The Atlantic is currently in an active phase which began around the mid-1990s. So, certainly, the record shows an increase in the frequency and intensity of TCs since the 1970s. But this does not mark an overall increase – it is just a part of the decadal cycle. Further, according to the IPCC’s latest report, there is low confidence that this increase is due to human-induced climate change. In other words, there is an 80% chance that this increase is not due to climate change.

So, the IPCC, and by extension, the UN is clear about the impact of climate change on TCs – it is currently “unlikely” having any effect on TC intensity. The same IPCC indicates that it is unequivocal that man is changing the climate. This is a position shared by over 99% of climate scientists and people in general. If we believe this part of the report, we must believe the part that speaks about the impact or lack thereof, at this time, of climate change on TCs.

This research position also shared by WMO and the TC research community.

Will TCs become more intense?

According the IPCC AR5, “more likely than not”. Going forward, IPCC AR5 says that climate change will “more likely than not” cause changes in TC intensities late in this current century – near year 2100.

This conclusion by the IPCC is consistent with one of the most authoritative scientific papers on the subject written by Knutson TR, McBride JL, Chan J, et al.. It says that late in this century, not now, based on models, there will be a 2 to 11% increase in wind speeds of TCs.

Empirical Data and the impact of climate change on TCs

Let’s look at the empirical data to see what they say regarding the impact of climate change on TCs. Based on the https://coast.noaa.gov/hurricanes/ database, the following is true:

CountOfHurricanes1924-1969VS1970-2016

A count of the number of hurricanes – 1924 to 1969 vs. 1970 to 2016. The bracketed numbers are the yearly averages.

From the above, clearly, there is no significant difference between numbers for the period 1924-1969, when climate change was not an issue, and the period 1970-2016, when climate change became an issue. What is interesting is that the numbers for 1924-1969 would have been higher, if not for a number of TCs being missed, due to a lack of satellite technology prior to the mid-1960s.

Further, some of the most powerful hurricanes to form across the Atlantic Basin occurred when climate change was not an issue – before the mid-1980s. Hurricane Allen which still holds the record for the highest maximum sustained wind speed ever on record over the Atlantic occurred in 1980. Of the top 12 strongest hurricanes, in terms of maximum sustained winds, six occurred before the mid-1980s.

Based on the IPCC and the vast majority of the TC researchers, TCs are an unworthy poster child for climate change. By the preponderance of research papers, climate change has NOT caused TCs to be stronger. Climate change had nothing to do with the strength of Hurricanes Irma and Maria or the activity of the 2017 Atlantic hurricane season. It is all due to natural variability.

However, by late this century “more likely than not” climate change WILL cause an intensification of TCs. But this is not yet evident. This is the conclusion of IPCC AR5 – we either accept the full report or none at all. And if we accept all of it, we would not be blaming hurricane intensities on climate change, at this time.

Our next blog in this series will look at the impact, if any, of climate change on tropical cyclone frequencies.





Tropical Cyclones and Climate Change

28 09 2017

Dale C. S. Destin |

With the current Atlantic hurricane season being hyperactive, thus far, and several countries being severely impacted by hurricanes, tropical cyclones (tropical depressions, tropical storms and hurricanes) continue to be made the “poster child” for the potential dangerous impacts of climate change.

Hurricane Irma - Sep 5-6, 2017. Travelling Across Barbuda and Anguilla.

Cat. 5 Hurricane Irma With Winds of 185 mph – Sep 5-6, 2017. The Eye travelled Across Barbuda and the Northern Leeward Islands.

This notion was crystallized by Former U.S. Vice President Al Gore on the cover of his book – “an inconvenient truth”, when he depicted a tropical cyclone (TC) spinning out of smoke stacks. Since then, several world leaders have supported this view, including former U.S. President Barak Obama, who said that “storms [are] growing stronger with each passing hurricane season”.

Over the years, many Caribbean leaders, have also joined in asserting that TCs have become stronger and more frequent due to manmade, greenhouse gas caused climate change. According to Prime Minister Gaston Browne of Antigua and Barbuda, “hurricanes are stronger and bigger because they are absorbing moisture from increasingly warmer seas, caused by global warming.” Browne’s colleague, Prime Minister Roosevelt Skerrit of Dominica supports this view and is convinced that Hurricane Maria is the product of climate change. He told the recent United Nations General Assembly that Maria was a climate change “truth we have just lived”.

Cat. 5 Hurricane Maria - 10:30, Sep 18, 2017- Eye Over Dominica.

Cat. 5 Hurricane Maria With Winds of 160 mph – 10:30 pm, Sep 18, 2017 – Eye Over Dominica.

There is no doubt that climate change is real and is happening. There is much evidence to point to. Contrary to the current U.S. President’s assertion, it is NOT a hoax created by the Chinese. However, do TCs deserve this poster-child position? How have TCs responded to manmade climate change? How will TCs respond to future climate change? Are there any doubts as to cause of Hurricanes Irma and Maria?

How have TCs responded, and how will they respond to human-induce climate change are topics of intense interest and public and scientific debates. Over the next few blogs, I will use the latest peer-reviewed scientific papers to answer these and related questions.

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The Advent of Potential Tropical Cyclones – What, When and Why?

21 06 2017

Dale C. S. Destin |

History was made this past Sunday when for the first time ever the U.S. National Hurricane Center (NHC) issued tropical storm (TS) warnings for portions of the southern Caribbean, in the absence of a TS. This they were able to do by designating an approaching tropical disturbance a “potential tropical cyclone” (PTC).

PTC_Bret

In the past, it was the policy of the NHC to not issue tropical cyclone (the generic term for tropical depressions, TSs and hurricanes) watches and warnings UNLESS there EXISTS a threatening tropical cyclone (TC). This was the case even if there was a 100% certainty that one was going to form and impact land in a short space of time.

This policy served us well. However, just about every year, there would be, at least, that one tropical disturbance that would approach land, and everybody knew it was going to form into a TC just before impact. But the existing policy would get in the way of issuing watches and warnings that were needed to sprung persons into meaningful preparations.

A classic example of this was Hurricane Tomas of 2010. The system approach the southern Caribbean in late October and was not upgraded to a TS until it was less than 12 hours away from Barbados.

TOMASAsTropDisturbance2010

Tomas as a potential tropical cyclone on the “doorsteps” of Barbados, less than 9 hours before impact, with no warning issued

So instead of having 36-48 hours lead time to prepare, there was less than 9 hours. The bulletin announcing the warnings not only came late but also late in the day – 5 pm, which means any preparations that could be done, took place mainly after-dark, after it started to rain and after hardware stores were closed.

Tomas cause eight deaths and over US$500 million dollars in damage across the southern Caribbean. Some of the loss could have been avoided if many persons were not caught off guard due to the very short lead time between the formation of Tomas and its impact on the islands.

Hurricane Gonzalo of 2014 similarly caught many Antiguans off guard and unprepared. Many persons did not hear about the system until hours before it arrived. One person told me that she suffered damage to her property because she only found out what was happening when the winds started to pick up. By then, it was to late for her to go outside to close the shutters. Many boats were damage or sunk because of insufficient time to secure them.

Gonzalo_AsAPotentialTropCyclone

Gonzalo as a potential tropical cyclone less than 20 hours before it made landfall in Antigua as a hurricane with no warning issued

To solve this problem, the NHC has revised its policy and instead of just issuing watches and warnings for ONLY existing TCs, they have started this year to issue them for “PTCs”. By definition, according to NHC, a PTC is: ”…a disturbance that is not yet a TC, but which poses the threat of bringing TS or hurricane conditions to land areas within 48 hours.”

So, no longer is a disturbance, with a high chance of becoming a TC, allowed to march up to a country without 24-48 hours of watches and warnings being issued. Such systems can now be declared PTCs and the requisite watches and warnings will be issued, early.

It could be argued that an approaching tropical disturbance with a high chance of becoming a TC should be enough to spring persons into TS or hurricane preparations. However, studies have shown, a great number of persons just don’t prepare until watches or warnings are issued. Hence, the need for them to be issued early.

This policy change may be one of the most important ever by the NHC. Like the previous policy though, this one is not perfect; however, it plugs a huge loophole in the TC warning system. It has the distinct potential benefit of further reducing “surprised” attacks from TC, which translate into saving more lives, more properties and livelihoods.

Notwithstanding, it has the potential to create some unnecessary stress. This will be so when disturbances designated PTCs do not actually become cyclones. I expect, this be a rare occurrence. In any event, preparations for PTCs are deemed low-regret actions at worse.

Happily, we are off to a good start. The historic first PTC became TS Bret less than 6 hours before making landfall in Trinidad. Under the old policy, many persons would have been caught off guard and unprepared, not so this time around.

EarlAsATropDisturbanceAugust2016

Earl as a potential tropical cyclone forecast to be near or over Jamaica in a day or two with no watch or warning issued

This new policy may have been hastened into being by the actions of the Jamaica Meteorological Service (JMS) last year, as it related to TS Earl. Whereas the NHC made history by issuing its first TC warnings based on a PTC, they were not the first to do so. The JMS, quite bravely, “took the bull by the horn” and made the tough, unprecedented but right decision to issue TS warnings for Jamaica in the face of TS Earl of 2016, when it was what we are now calling a PTC, approaching the island.

So, well done to Jamaica for setting the stage for the first ever PTC bulletin by NHC – both are a success stories – mission accomplished, congratulations!





The 2017 Atlantic Hurricane Season Early Forecast

7 04 2017

Dale C. S. Destin |

Good news! The early forecasts just issued for the upcoming 2017 Atlantic hurricane season (AHS) indicate a below normal season is most likely. This is forecast to be most evident in the number of hurricanes that forms (see graphic below). It could be as quiet as the 2014 and 2015 seasons. Nevertheless, the usual complete preparations are still very much required.

Ensemble forecast

The ensemble (mean) forecast, based on predictions from Klotzbach of Colorado State University, Saunders and Lea of Tropical Storm Risk.com (TSR) and AccuWeather.com, is for 11 named storms, 4 becoming hurricanes and 2 becoming major hurricanes.

2017HurricaneSeason

A better indicator of the activity for the season is the accumulated cyclone energy (ACE) index which is a measurement of the strength and duration of each tropical cyclone. Summing together the ACE of each cyclone, provides a more complete picture of how active the season is likely to be outside of just the number of storms.

This year, the ensemble forecast calls for an ACE index of 71. If this forecast pans out, the 2016 season would be around 30% less active than normal.

It must be noted though that there is very low skill in forecasting the AHS (June to November) in April. However, this is the best available forecast for the season, from this vantage point, and can be used as a guide for what is possible. A more skilful forecast will be available around June 1.

El Nino

 The development of an El Nino is the main climate factor that is forecasts to cause the hurricane season to be quieter than normal. El Nino is virtually synonymous with inactive AHSs, as it causes unfavourable conditions for tropical cyclones (tropical depressions, tropical storms and hurricanes). The main one being the creation of strong winds aloft that inhibits or rips tropical cyclones apart.

However, regardless of the above probabilities and forecasts, this is not a licence to do anything differently for this hurricane season. The same comprehensive preparations are required to deal successfully with any eventuality. It only takes one tropical cyclone to set you back for years. Recall – Gonzalo struck us in a quiet year – 2014.

New and improved products

As is the case annually, there are new and improved products that will be on show. The most significant of which will be the issuing of watches, warnings and advisories for potential tropical cyclones.  A potential tropical cyclone is being defined as a disturbance that has the potential to produce tropical storm or hurricane conditions to land areas within 48 hours.

This new product is expected to be a game-changer as it will eliminate surprise storms and hurricanes and increase the lead time for preparations for rapidly developing disturbances approaching land. If such a product were in place for Gonzalo of 2014, Antigua would have likely fared much better.

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2016 hurricane season summary

The 2016 AHS was active – the first active (above normal) season since 2012 and the most active since 2010, based on the ACE index. It produced 15 named storms. Of the 15, 7 became hurricanes and 4 reached major hurricane status – at least Category 3 on the Saffir-Simpson Hurricane Wind Scale. The strongest tropical cyclone for the season was Major Hurricane (MH) Matthew with peak winds of 160 mph and minimum pressure of 934 millibars.

Hurricane Matthew caused the most devastation. In total, up to 600 deaths have been attributed to the storm, including over 500 in Haiti, making it the deadliest Atlantic hurricane since Stan in 2005.

The 2016 season is the first year since 2008 no tropical cyclone passed within 121 miles of Antigua. It was likely the least stressful AHS for the island in, at least, eight years.

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