Climate Change and Tropical Cyclone Forward Speed

26 01 2020

Dale C.S. Destin|

Many have made tropical cyclones (hurricanes, tropical storms and tropical depressions) the posterchild for climate change with respect to how they are or may be responding to a warming climate. It is a hot topic of debate that researchers are continuously investigating for answers. One of the many questions been asked is, “Are global tropical cyclones moving slower in a warning climate?”  

The track of Hurricane Irma – 2017

A recent research letter, in the Institute of Physics (IOP) Publishing, by Kelvin T.F. Chan, of the School of Atmospheric Sciences, and Guangdong Province Key Laboratory for Climate and Natural Disaster Studies, Sun Yat-sen University, Zhuhai, People’s Republic of China, weighed in, quite forcefully and persuasively, on the above question.

Time series of annual-mean global tropical-cyclone translation speed and their linear trends in periods 1949–2016 (blue) and 1970–2016 (orange).

According to Chan, the short answer to the question is no. Chan successfully show that, with the use of reliable data from 1970 to 2016, there is no significant change in the forward speed of tropical cyclones, notwithstanding the pronounced warning of the globe seen over the last half-century.

Chan’s finding virtually contradicts a 2018 paper present by James P. Kossin of the NOAA National Centers for Environmental Information, Center for Weather and Climate, Madison, WI, USA. Kossin found that there was a 10% slowdown in global tropical-cyclone translation (forward) speed over the past 68 years – 1949 to 2016. His implication was that this was related to anthropogenic climate change.

The IOP letter, by Chan, successfully shows that the findings of Kossin was based on the use of widely accepted spurious data obtained prior to the satellite era – pre 1966. Unanimously accepted, more accurate data since the satellite era – 1970 to 2016, show no significant slowdown of tropical cyclones. Understandably, prior to weather satellites in 1966, accurately tracking tropical cyclones was very difficult to impossible; hence, translation speed data before then are highly unreliable.

This finding of Chan is consistent with the findings of Knutson et al, in a very comprehensive study on the entire subject of climate change and tropical cyclones. According to Knutson, the results for the models “indicate no significant changes, and only 2 of the 10 individual… model projections show a significant change (increase).” He concluded that there was no clear consistent trend in the forward speed of tropical cyclones.

The question of how climate change is or may impact the forward speed of tropical cyclones is very important from a adoptation standpoint. A slower moving tropical cyclone has the potential for more destruction and vice versa. Naturally, the longer a tropical cyclone hangs around a particular populated area, the more the destruction is likely to be via wind, flooding rainfall and storm-surge.

Intuitively, it would be consistent to think that since a warning climate is slowing down the circulation of the tropics, it is also slowing down tropical cyclones, embedded its circulation. However, this is clearly not happening, certainly not based on the data since 1970 to 2016.

Tropical cyclones may be the posterchild for climate change; however, there is no evidence to support any changes in tropical cyclones forward speed, due to the changing climate being forced by humans.  

More broadly, there exist no evidence that there have been any changes in tropical cyclones, due to anthropogenic climate change. However, that is not to say that climate change won’t have an impact on tropical cyclones in the future.  

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Bomb Cyclone to Push Damaging Swells Across the Caribbean

16 01 2020

Dale C.S Destin|

The Caribbean Basin is about to see another round of large and damaging swells reaching its shorelines starting Saturday, from a bomb cyclone. Swells are forecast to exceed 3.5 metres (12 feet) and break at higher heights, as surfs, on coastlines. This is likely to be the biggest swell event since Swellmageddon of March 2018.

Animation of bomb cyclone, east of Canada, with pressure pattern, wind speeds and directions, as forecast by the Global Forecasting System (GFS) Model. Time in UTC

The event will be kicked off by a relatively inconspicuous low-pressure system (LPS), currently over the northeast United States. The LPS will go through explosive development (bombogenesis) over the next 24 hours and become a ginormous and powerful bomb cyclone (extratropical cyclone) over the northwest North Atlantic, with hurricane-force winds.

Although this system will form over 3220 km (2000 miles) away, it will have a significant impact on the region, through its strong winds pushing unusually high waves to our shores. The first set of these swells will reach the Bahamas on Saturday; the northeast Caribbean, including Antigua and Barbuda, on Sunday and the Guianas on Monday. The event will likely last three days from its start time. So, for the northeast Caribbean, its Sunday through Tuesday.

Animation of swells forecast to move across the region from the bomb cyclone, as predicted by the European Centre for Medium-Range Weather Forecasts (ECMWF) wave model (WAM). Time in UTC.

Swells will rise to to in excess of 3.5 metres across most of the Atlantic waters of the islands. There swells will produce even higher surfs or breaking waves. These surfs could be as much as twice the height of the incoming swells, depending on the bathymetry/topography of the near shore seafloor. This is expected to cause beach closures, as swimming conditions will become quite hazardous. Other impacts include:

  • major beach erosion;
  • flooding of some low-lying coastal roads;
  • disruptions to marine recreation and businesses;
  • disruptions to potable water from desalination;
  • damage to coral reefs and
  • Financial losses.

Advisories and warnings will be required for the weekend and or the first half of next week. The event will also be felt along the East Coast of the United States, Canada, Greenland, Iceland, the United Kingdom and Norway. Rowers of the Talisker Whisky Atlantic Challenge will also be negatively impacted, exponentially increasing the challenge of an already very challenging race.

High surf warnings or advisories will be required for coastal areas for much of the Caribbean this weekend and into the middle of next week

The impact on shorelines will not be the same everywhere. Depending on the depth and the natural shelter of the coastal waters, the impact will be different. Moderately sloping, shallow, north and or north-facing shorelines are expected to see the highest swells and surfs.

The bomb cyclone will go from a central pressure of 1004 hectopascals (hpa) (which is the same in millibars) to around 968 hpa in 24 hours and to a minimum of 955 hpa in 48 hours, just east of Newfoundland and Labrador, Canada. This represents an explosive drop of 59 hpa – more than one hpa per hour; thus, meeting the definition of a bomb cyclone – a drop in pressure of an extratropical cyclone of at least 24 hpa in 24 hours or less.

By Saturday, this weather bomb will be packing Category 1, hurricane force winds – 119 to 153 km/h (74 to 95 mph). These are the winds that will, in turn, generate large waves that will traverse the Atlantic and pound the shorelines of the Caribbean, inundating some low-lying coastal areas.

Of course, the hurricane force winds do not even have the remotest of chance of reaching the Islands; however, some of the wind energy, transferred into the seas will reach us in the form of ocean waves – ground swells. As you may know, waves do not transport water; they transport energy, which can de destructive when they break on shorelines.

Animation of wind directions and speeds forecast to impact the region, as predicted by the ECMWF Integrated Forecasting System (IFS) Model. Time in UTC.

Talking about winds, they are expected to surge – getting to the general range of 25 to 45 (16 to 28 mph), across the region again late Saturday and likely continue into Monday. Storm-force gusts to near 65 km/h (40 mph) are expected, especially in showers. Thus, both high wind advisories and small craft warnings are highly possible late Saturday through Monday morning.

Our (Caribbean) weather will also become wet again over the weekend and into midweek. There is a very high chance of occasional brief showers, as the high winds will destabilise the atmosphere via mixing and low-level convergence.

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Strong Howling Winds to Continue to Impact the Caribbean

11 01 2020

Dale C.S. Destin, updated January 12, 2020 |

Strong howling winds are expected to continue across much of the Caribbean Basin through Tuesday. These huffing and puffing, big bad wolf winds are causing notable socio-economic impacts to the islands.

As the winds go up, so also do the seas; hence, hazardous seas have engulfed the region – from the Bahamas to the Guyanas, including the Caribbean Sea.

The winds have risen to the range of 29 to 52 km/h or (18 to 32 mph) over land and are expected to persist until Tuesday. Further, gusts as high as 80 km/h (50 mph) are possible for some areas. Over the Caribbean Sea, the winds are forecast to be stronger than some places over land. One such area is between Jamaica and Columbia, where sustained winds – 70 km/h (44 mph), are forecast. With respect to land, the highest sustained winds are forecast for the Eastern Caribbean.

The blustery winds will cause the seas to remain very angry with significant wave heights of 2.5 to over 4 metres (8 to 14 feet) and occasionally reaching over 5 metres (18 feet). There is an area between Jamaica and Columbia where the significant wave heights are predicted to be over 5 metres (18 feet), occasionally reaching 7 metres (23 feet).

Over the past 24 hours, above normal swells, from distant strong winds, have added to the hazards across the area. So, not only there are concerns for high winds and hazardous marine conditions in open waters, there is now also a concern for the impact of life-threatening surfs (breaking waves) along, mainly northern and north-facing shorelines; hence, a high surf advisory has or will be required for most islands. Already, a high surf advisory is in effect for much of the Caribbean.

Beachgoers should be extremely cautious; bathe only where lifeguards are present or the sheltered, less affected beaches, mainly to the south. See the bulletins from your national weater service for detail and specific guidance for you local.

Such conditions are very conducive fo rip currents – powerful channels of water flowing quickly away from shore, which occur most often at low spots or breaks in the sandbar and near structures such as groins, jetties and piers. If caught in a rip current, relax and float. Don`t swim against the current. If able, swim in a direction following the shoreline. If unable to escape, face the shore and call or wave for help.

As a result of the weather, more so the strong winds, three cruise ships had to abort berthing at the St. John’s Harbour in Antigua. These, I am informed, were The Anthem of the Seas, Norwegian Dawn and Crown Princess. Ferry service between Antigua and Montserrat has been cancelled until Thursday. The have also been aborted attempts by LIAT to land in Dominica. There are also reports of downed banana and other trees in the Windward Islands and Trinidad and Tobago, and there have been power outage in the British Virgin Islands and Trinidad and Tobago attributed to the strong winds.

Thus far, the highest winds (10-minute sustained and gusts) have been observed at:

  • Grantley Adams International Airport (GAIA), Barbados;
  • George F.L. Charles Airport (GFLCA), St Lucia and
  • Norman Manley International Airport, Jamaica.
The winds by the numbers. One mph = 1.61 km/h. Multiply 10-minute sustaned winds by 1.11 and 1.40 to get 1-minute sustained winds and 3 second gusts respectively. *Harper et al. 2010 is the World Meteorological Organization (WMO) standard.

Looking at the winds by the numbers. Speeds of 39 mph or more are storm-force or gale-force winds, gusts in this case. However, when dealing with tropical cyclones, categorization is based on a maximum 1-minute sustaned wind speed. To convert from 10-minute wind speeds to 1-minute wind speeds, multiply by 1.11. Thus, parts of Barbados, Jamaica and St. Lucia had sustained storm-force windsstorm conditions (35×1.11 = 39 mph or 63 km/h). However, note that there are no tropical cyclones in the area.

Winds blow because of the differential of pressure across the Earth’s surface. The higher the horizontal differential or the higher the pressure gradient, the stronger the winds. The strong winds, over the next several days, will continue to be due to a very steep pressure gradient. The pressure will be that steep largely due to a 1042 millibar high-pressure system moving off the US east coast.

Pressure pattern forecast for 2 am Saturday, January 11, 2020
The ususal pressure pattern across the North Atlantic for January. Note that the usual difference of pressure between Bermuda High and the Caribbean is around 6 to 8 mb.

Immediately above is the usual pressure pattern for the North Atlantic. Note that the usual difference in pressure between the Bermuda High and the Caribbean is around 6 to 8 millibars. However, compare the graphic below to the one above and you will observed that the difference in pressure between the Bermuda High and the Caribbean (at 2 am, Sat, 11 Jan 2020) was 20 to 24 millibars. Thus, the pressure difference and gradient were two to four times higher that usual or 200 to 400% of normal; hence, the very strong winds.

North Atlantiuc surface chart – 2 am, Saturday, 11 January 2020

The highest and most dangerous waves will take place across the waters of the western Caribbean – between Jamaica and Columbia. This area will also experience the strongest winds – 51 to 64 km/h (32 to 40 mph), gale-force/storm-force winds, with gusts in excess of 96 km/h (60 mph).

Advisories and or warnings to mariners have been issued by a number of islands, including Antigua and Barbuda, Puerto Rico and Barbados.

As a small craft operator, if an advisory is issued – inexperienced mariners, especially those operating smaller vessels should avoid navigating in these conditions. If a small craft warning is issued – you should stay in or very near port.

Potential impacts from this hazardous sea event include injuries or loss of life, damage or loss of boats and fishing equipment and disruption to sea transportation. Other possible impacts comprise of:

  • disruptions to sea search and rescue;
  • scarcity of seafood;
  • disruptions to off shore marine recreation and businesses;
  • business and economic losses.

On the other hand, the strong winds could result in further disruptions to transportation and outdoor sporting activities, soil erosion, vehicular accidents and financial losses.

Please share my blog, if you find it useful and keep following it and my other media – TwitterFacebook and Instagram for more on this windy issue and all things weather and climate.








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