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Atlantic Hurricane Season

2020 hurricane season arrives early and could be record breaking.

15th May and 1st June mark the traditional start of the hurricane season in the Eastern Pacific and North Atlantic respectively and lasts until 30th November. No one season is identical to another as weather patterns are constantly changing, plus there is now climate change to consider with the ever growing threat of more extreme events as the atmosphere continues to warm up. With 3 hurricanes occurring ahead of the official start date already this year’s season will likely be more challenging than normal. 

Tropical Depression (TD) One-E formed in the East Pacific on April 25 and became the first April TD and earliest formation of a tropical cyclone on record in that ocean. In the Atlantic, Tropical Storm Arthur formed 16 May marking the sixth consecutive year with an Atlantic storm occurring before the official start date. The second -Tropical Storm Bertha – was upgraded to storm status by the National Hurricane Center (NHC) on 27 May 1330UTC and made landfall around 1430UTC on the same day near Mount Pleasant, NC. In doing so, the time span of just one hour between Bertha’s designation and making landfall is one of the shortest on record.  

Records show there have only been four other years where two systems have been recorded to have reached named-storm strength prior to the June 1 start date. While records go back to 1851 for the Atlantic they are less reliable until satellites were introduced in the 1960s.

Unusually for 2020 there is greater consensus than normal by the various agencies, institutions, and private forecasting companies that this season is predicted to be above average. The experts are predicting 17 Named Storms, 8 hurricanes and 3-4 Major (Category 3 +) Hurricanes, and NOAA’s predictions support this consensus too. This follows the 2019 season which marked the fourth consecutive year of above-average activity and tied with 1969 for the fourth most-active hurricane season on record. More poignantly, it was also the fourth consecutive season to produce Category 5 Hurricanes with Dorian and Lorenzo.  

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Tropical cyclones/hurricanes are already the most powerful weather events on Earth. While the jury is still out on whether global warming will result in more hurricanes, there is clear evidence that hurricane intensity, size and rainfall rates will increase as the climate warms up.

There are multiple factors to consider when creating a seasonal hurricane forecast but the greater consensus for 2020 is due to the combination of above normal sea surface temperatures in the Atlantic and Gulf of Mexico, high confidence that El Nino will not inhibit hurricane activity, weaker tropical Atlantic trade winds and an enhanced west African monsoon. Most forecast models indicate either a neutral or even La Nina conditions for the peak Atlantic season (August to October) which create a more favourable environment for tropical storm development with reduced vertical wind shear.

This season brings some updates by NOAA/NHC which Mariners should note. NHC will begin providing 60-hour track, intensity, and 34-kt and 50-kt wind radii forecasts which will be included on their cone graphic. Previously the centre used local time within the product header based on the time zone where the centre of the tropical cyclone is located. Beginning in 2020, systems located south of 25°N and east of 30°W will use Cape Verde Standard Time (GMT-1) and systems north of 25°N and east of 45°W will use Greenwich Mean Time (equivalent to Azores Summer Time). 

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The size of the tropical cyclone track forecast error cone for the Atlantic basin will be mostly unchanged this year.  The Eastern North pacific has some slight changes.  The cone represents the probable track of the centre of a tropical cyclone, and is formed by enclosing the area swept out by a set of imaginary circles placed along the forecast track (at 12, 24, 36 hours, etc.). The size of each circle is set so that two-thirds of historical official forecast errors over the  previous five years (2015-2019) fall within the circle. The circle radii defining the cones in 2020 for the Atlantic and eastern North Pacific basins are given in the table below:

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So, from a mariner’s perspective, the 180nm/5-day track error rule of thumb remains a useful number to keep in mind when route planning and considering forecast uncertainty. The intensity error is in the 10-15 kt bracket from 72-120 hours, so the NHC typically warns to prepare for one category stronger (on the Saffir-Simpson Hurricane Wind Scale).  

This article was originally posted on Linked In.

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