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 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 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.

Click here for other new and improved products.

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.

Follow us and stay updated on the 2017 AHS via our social media platform, which includes twitter, facebook, wordpress, instagram, tumblr, and google+. Follow us also for all things weather and climate.





Become Hurricane Strong by Taking Action Now

15 05 2016

Dale C. S. Destin |

The 2016 Atlantic hurricane season starts in 17 days – June 1, and runs until November 30. The season is forecast to have near normal activity – 13 named storms, 6 hurricanes and 3 major hurricanes.

Regardless of the forecast, the same detailed preparations are required to protect life, property and livelihoods. As we say in the meteorological community, it only takes one to change your life and community. Recall, notwithstanding last year’s hurricane season being quiet, Erika caused catastrophic damage to Dominica.

May 15-21 is designated hurricane preparedness week in the U.S. – the time to prepare for potential tropical cyclones (tropical depressions, tropical storms and hurricanes) over the upcoming six months. We have no such week here, but we have a shared enemy; hence, we need to prepare similarly. The following are the seven actions required now to become “hurricane strong” i.e. resilient to tropical cyclones.

Determine your risk from tropical cyclones. Disaster risk is inversely proportional to knowledge – meaning the more knowledge you have on the subject the lower your risk is likely to be. Depressions, storms and hurricanes are not just about high winds, other associated hazards are inland flooding, storm surge, rip currents and tornadoes. Know the potential hazards that could affect your location and prepare to mitigate them. Local knowledge could be crucial in this regard, so seek it, especially with respect to flooding (See our tropical cyclone climatology).

All Antigua Named Storms

All the named storms to have affected Antigua – 1851-2014. Credit NOAA

Develop an evacuation plan if you live in an area that will need to be evacuated or if your home is deemed unsafe to ride out a tropical cyclone. Public shelters should be a last resort, so try to arrange to have the home of a friend or relative as your evacuation destination, if need be.

Secure an insurance check-up to ascertain that you have adequate coverage for your home and content. You especially need to ensure that you have coverage for wind and flood damage – the two main destructive hazards of depressions, storms and hurricanes.

Assemble disaster supplies now so as to avoid long lines and potential scarcity before and after a tropical cyclone. This is one of the most important elements of being “hurricane strong”. Supplies should be enough to last for at least one week after the event and should include things such as non-perishable food items, water, portable radio and batteries.

Strengthen your home, if possible, to be able to withstand, at least, a Category 3 hurricane. The best place to ride out a storm is in your own home. So, if you have questions about its strength, get a qualified professional to evaluate it, and if it can be retrofitted, do it. In the long run, it will be far cheaper than going to a shelter and leaving your property to be blown away.

Identify your trusted sources of information for a hurricane event. Your national meteorological service is your most trusted source – in the Antigua and Barbuda context, it’s the Antigua and Barbuda Meteorological Service through its website and hotline: 4634638.

Trusted information can also be had from the following social media accounts:

Your disaster management agency, in our case – the National Office of Disaster Service (NODS) will provide disaster management services to reduce the risk of the inclement weather.

Both your met office and disaster management agency will partner with a number of media outlets to get the information out. For us, the Antigua and Broadcasting Service (ABS) will be foremost partner.

Complete your written hurricane plan now, before the hurricane season starts. The time to write your plan is not when you are steering down the barrel of a hurricane. Under such conditions, you are likely to forget crucial things or make the wrong decisions. Your written plan should include where you are going to ride out the storm and a communication strategy.

Start preparing for the hurricane season today and become “hurricane strong”. Follow us via social media for the latest updates.





Hurricane Season Again!!!

10 04 2014

By Dale C. S. Destin |

It looks like we may have a repeat of last year’s hurricane season. Early forecasts for this year’s Atlantic hurricane season indicate that it could make it two seasons in a row of quiet conditions. That would be a relief to many residents of Antigua and the Caribbean.

According to the UK-based Tropical Storm Risk (TSR), the Weather Channel (WC) and Colorado State University (CSU), the consensus is for around 11 named storms of which four will become hurricanes and two major hurricanes – Category 3 or stronger – this hurricane season. Those numbers are pretty normal. Based on the period 1950-2012, the hurricane season usually generates 11 named storms, six hurricanes and three major hurricanes.

Notwithstanding, the consensus of TSR and CSU is that the accumulated cyclone energy (ACE) index going to be roughly 35% below average. The ACE index is the measurement that takes into account the strength and duration of each tropical cyclone. Summing together the ACE of each cyclone, provides a snapshot of how active the season was outside of just the number of storms.

If these forecasts pan out, the 2014 hurricane season would be the fourth quietest since 1995, when the hurricane season went from a quiet phase to an active one. The average ACE since 1995 is 134, whereas, the ACE for 2014 is predicted to be 65 by consensus. This would also make this the quietest two year period since 1995.

However, the TSR forecast, in particular, was quick to point out that there are large uncertainties as to how the season will actually play out and the forecast skill, for this time of the year, is very low.  In fact, last year’s early season forecasts offer a cautionary tale. The main factors pointing to an inactive hurricane season are the likelihood of El Nino and cool tropical Atlantic sea surface temperatures (SSTs).

Busted Forecasts

Last year was a major failure for hurricane season forecasters. Of the dozen or so forecasts issued, all were “a complete bust”. This came as a surprise as the tropical Pacific SSTs was average to slightly cool and the tropical Atlantic SSTs were warmer than normal. More often than not, this is a recipe for an active Atlantic hurricane season. Admittedly though, although not perfect, these forecasts normally perform much better.

2013 Hurricane Season Tracks

2013 Hurricane Season Tracks

Overall, there were 14 named storms, but only two became hurricanes. Both were weak Category 1 hurricanes.

Despite the slightly above normal number of named storms, the 2013 season tied with 1982 for the record fewest hurricanes since 1950. And 2013 was the first time since 1994 that there were no major hurricanes, something that’s only happened three other seasons since 1950, (1968 1972 1986). Further, this was the first time since 1968 that an Atlantic hurricane season failed to produce a Category 2 hurricane. Also telling was the season’s ACE index score, which is just 30% of the 1950 – 2012 average.

The Blame for Last Year

The low activity in 2013 is being blamed on an “unpredictable atmospheric pattern that prevented the growth of storms by producing exceptionally dry, sinking air and strong vertical wind shear in much of the main hurricane formation region, which spans the tropical Atlantic Ocean and Caribbean Sea,” said Gerry Bell, lead seasonal hurricane forecaster at NOAA. Bell also said that “detrimental to some tropical cyclones this year [2013] were strong outbreaks of dry and stable air that originated over Africa.”

Similar explanations for the notably quiet season have also come from other scientists such as Chris Landsea, a meteorologist at the US National Hurricane Center and Philip Klotzbach, a hurricane researcher and seasonal hurricane forecaster at CSU.

Klotzbach also said that recent research has led researchers to “attribute a sizeable portion” of the negative hurricane conditions to the springtime weakening of the Atlantic Ocean overturning circulation. He said that a strong circulation favours high activity and a weak circulation favours low activity. According to Klotzbach, the 2013 spring circulation dropped to the “weakest since 1950.” There is ongoing research by other organizations to better understand the factors that contributed to the almost hurrcaneless season.

Hurricane Drought Continues

TS Chantal moving through the Caribbean - 2013

TS Chantal moving through the Caribbean – 2013

The 2013 season marks the 14th consecutive year of our hurricane drought. Since Jose and Lenny both made landfall in Antigua in 1999, the island has been spared from hurricane-force winds.

TS Chantal's Tornado

TS Chantal’s Tornado

This is not to say that the island has not been affected by any tropical cyclones since 1999 but rather none has caused any winds in excess of 73 mph to affect the country. This was also the first time since 2005 that no storm passed within 120 miles of Antigua. But of course, winds are not the only threat from tropical cyclones. Last year, we experienced one of the rare threats in this part of the world. Although Tropical Storm Chantal passed about 178 miles to the south, it spawned a tornado which proved destructive to Camp Blizzard.

Consecutive quiet hurricane seasons are most welcome. And although some may have felt letdown by the failure of the forecasts last year, most of us were ecstatic that the season was very slow. Over the next days and months, other organizations will issue their take on the 2014 season, which runs from June 1 to November 30. We look forward with bated breath to similar or better (lower) numbers. However, it is important to remember that regardless of the number of storms forecast for the season, it only takes one to ruin our year, so be prepared. I will keep you posted.

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