Dale C. S. Destin|
Recently issued updated forecasts for the 2015 hurricane season, which started June 1, reiterated another quiet season is highly likely. The latest set of updated forecasts are similarly calling for this season to be even quieter than 2014 and perhaps be among the top 10 quietest on record.
The updated 2015 ensemble forecast
The updated ensemble or mean forecast is for nine named storms (including Tropical Storm Ana, Bill and Claudette), four becoming hurricanes and one becoming a major (Category 3 or higher) hurricane. On average we get twelve named storms, four hurricanes and three major hurricanes.
Our ensemble forecast is based on forecasts from Klotzbach and Gray of Colorado State University (CSU), the National Ocean Atmospheric Administration (NOAA), Saunders and Lea of Tropical Storm Risk.com (TSR) and European Centre for Medium-Range Weather Forecasts (ECMWF).
The indicator of the activity used by meteorologists is the accumulated cyclone energy (ACE) index which is a measurement that takes into consideration the number, strength and duration of tropical cyclones (storms and hurricanes) for the season.
The ensemble ACE index forecast for this season is 44, down from 52 indicated in June and 61.35 below the normal/average. If this forecast verifies, this hurricane season will be the tenth quietest since 1981 and the third quietest since 1995.
The season thus far
Ana was a preseason storm and now holds the record for the earliest tropical cyclone to strike the United States. Antigua has never had a tropical cyclone in May but had a hurricane in January 1954 and March 1908.
Why is a quiet season expected?
El Nino is expected to be the main cause of a quiet season. El Nino has strengthened over the past months and has reached the threshold to be categorized as strong.
History has shown that the stronger an El Nino,, the more difficult it is for tropical cyclones to form over the Atlantic. This year we could see what is referred to as a super (strong) El Nino which would make it super difficult for tropical cyclones to form.
Past times have also shown that cool sea surface temperatures (SSTs) across the tropical North Atlantic (TNA) makes it hard for tropical cyclone formation. As of July, SSTs in the TNA were around 0.5 °C below average; hence, cool unfavourable tropical cyclone conditions exist and should remain this way for much of the next three months.
Another limiting factor for tropical cyclone formation is the more than usual flow of very dry, dust Saharan air across the TNA. This almost makes it impossible for tropical cyclone to form in their favourite area – between Africa and the Caribbean. However, it is uncertain if this flow will continue.
Combined, we may be witnessing one of those rare occasions when all the ingredients are in place to cause one of the quietest hurricane seasons on record.
Probability of Antigua being hit by a hurricane
Based on the ENSO record dating back to 1950, we have never taken a hit from a tropical storm or hurricane during an El Nino episode that has occurred over any part of the hurricane season, and this year is expected to be no different (“knock wood”).
According to Klotzbach and Gray, the best similar/analogue years to June-July 2015 hurricane season are 1965, 1972, 1982, 1987 and 1997. Of these years, only Erika brushed us in 1997. Thus, based on similar years, the probability of Antigua being affected this year, by a storm or hurricane, is around 18%, an increase of 3% from the June and the same as what was issued in April.
Don’t be caught off guard
Quiet season or not, we cannot let our guards down. Recall last year’s season was quiet, yet we were rough up by Hurricane Gonzalo. Stay prepared especially since we are in the peak of the hurricane season, August-October.
The hurricane season runs from June 1 to November 30 each year.