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.

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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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A Hyperactive 2017 Atlantic Hurricane Season Thus Far

1 09 2017

Dale C. S. Destin |

We are at the halfway mark of the 2017 Atlantic hurricane season and it has been a hyperactive one with respect to named storms. On average, the first half of the season produces four named storms; however, this year it produced nine – more than doubled the amount. The last time there were 9 named storms by the end of August was 2012. Also this has only happened 5 times in the last 82 years.

2017HurricaneNames_Sep2017

Ensemble forecast

Most of the forecasts for the season are on track. The ensemble (mean) forecast, based on predictions from yours truly, the Integrated Forecast System of the ECMWF, the National Oceanic and Atmospheric Administration (NOAA), Klotzbach of Colorado State University and Saunders and Lea of Tropical Storm Risk.com (TSR) is for 17 named storms, 7 becoming hurricanes and 4 becoming major hurricanes.

Hurricane Season Forecast 2017

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 or likely to be outside of just the number of storms.

Thus far, the ACE is 29. This is relatively low and is indicative of the weak and short-live nature of the storms so far. The forecast is for a further 108 ACE over second half of the season. For the whole season, the ensemble forecast calls for an ACE index of 136. If this forecast pans out, the 2017 season would be around 30% more active than normal and the highest in seven years.

Tropical North Atlantic

The tropical North Atlantic is almost catching fire. It is the warmest June to August since 2010 and the third warmest on record dating back to 1948. The very warm sea surface temperatures are the main reason for the more than doubling of the number of named storms normal for up to this time of the year.

Probability of Antigua being hit by a hurricane

According to Klotzbach, the likely best similar years to the upcoming 2017 AHS are 1953, 1969, 1979, 2001 and 2004. Over these year, we were affected by four named storms with one being a major hurricane. Thus, based ONLY on similar years, the probability of Antigua being affected by one or more named storms is around 54%, up 5% fro the average. However, the probability for one or more hurricanes is around 2%, down by 20% from the average. Notwithstanding, as I write, there is Category 3 Hurricane Irma tracking towards the island, causing a great scare.

We are in the peak of the hurricane season – keep monitoring and complete your hurricane plan, just in case you need to use it.

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Tropical Storm Bret 2017: Firsts or Firsts in a Long Time

9 07 2017

Dale C. S. Destin |

Tropical Storm Bret making landfall on Trinidad during the early morning hours of June 20, 2017.

Tropical Storm Bret making landfall on Trinidad during the early morning hours of June 20, 2017.

The formation of Tropical Storm Bret, a few weeks ago, resulted in several firsts or firsts in a long time for the Atlantic hurricane season, for the Eastern Caribbean and for Trinidad. Here are some we have noted:

  • 1st named storm to pass south of La Brea, Trinidad.
  • 1st named storm to form between Africa and the Caribbean before summer (June 21).
  • 1st time there were two named storms (Bret and Cindy) in June alive at the same time – June 20, 2017.
  • 1st designated potential tropical cyclone ever by the U.S. National Hurricane Center.
  • 1st named storm to impact the Eastern Caribbean before summer, since an unnamed hurricane in March 1908 impacted Antigua and the northeast Caribbean – the only other such system to impact the area before June 21; it formed in the Caribbean Sea.
  • 1st named storm to impact Trinidad in June since an unnamed hurricane in 1933. There is no other June storm on record for Trinidad.
All named storm on record for June - 1851 to 2016

All named storm on record for June – 1851 to 2016. Only three storms have affected the Eastern Caribbean in June since 1851. Two seen above plus Bret.

  • 1st named storm to form between African and the Caribbean in June since Tropical Storm Anna of 1979. There has ONLY been one other in June – an unnamed hurricane of 1933. So, there have ONLY been three named storms to impact the Eastern Caribbean in June on record.
  • 1st named storm to make landfall (pass over land) in Trinidad since Tropical Storm Bret of 1993. This has ONLY happened three other times – Fran of 1990, Alma of 1974 and an unnamed storm of 1933.
  • 1st named storm to pass within 65 nuatical miles (nm) or 120 km of Port of Spain, Trinidad, since Joyce of 2000. There have ONLY been 11 named storms in history, dating back to 1851, to have passed within 65 nm of Port of Spain, Trinidad; ONLY four were hurricanes, the last one being Hurricane Flora of 1963.
All named storms to have passed within 65 nm of Port of Spain, Trinidad on Record - 1851 to 2016

All named storms to have passed within 65 nm of Port of Spain, Trinidad on Record – 1851 to 2016

  • 1st time two named storms (Bret and Cindy) formed in June since 1909. It has happened ONLY two other times – 1906 and 1886. Both 1906 and 1886 turned out to be very active years; 1909 had near normal activity.
  • 1st named storm in June since Barry of 2013.

This June was quite active, in terms of named storms. The average for the month is 0.5 or one every other year. So, the two named storms which formed in this past June amount to the total we normally get in four Junes.

Is the activity of June an omen for the rest of the season? Well, the sample  size – three, is way too small to so say anything remotely definitive; however, FYI, of the three Junes with two named storms, two were quite active. Further, of the 10 seasons with at least 3 named storms forming between January 1 and June 30, six have been near or below normal.

All named storms for Jan-Jun 1851 to 2016

All Jan-Jun named storms on record, 1851 to 2016

Our most recent forecast of the season calls for above normal activity with 16 named storms, 7 becoming hurricanes and 4 becoming major hurricanes.

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Our Inaugural Forecast of the Atlantic Hurricane Season

5 07 2017

Dale C. S. Destin |

We have just released our first inhouse-produced forecast of the Atlantic hurricane season. It calls for an above normal season with 16 named storms, 7 becoming hurricanes and 4 reaching major hurricane status.

The main reasons for the above normal forecast are the warmer than usual tropical North Atlantic and the unlikely development of an El Nino. This season could turn our similar to last year’s and be one of the most active since 2010.

We hope that you find this forecast to be a useful resource in your hurricane season preparations. Please feel free to share you feedback with us as usual.  Click here for the full forecast.

Become hurricane strong!

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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!








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