John Tibbetts

By John Tibbetts
Director General
Cayman Islands National Weather Service

As we start to look at the upcoming hurricane season, it is critical to take a look back at the past season.

The 2020 Atlantic hurricane season was the most active, and the fifth costliest, Atlantic hurricane season on record, with 30 named storms, 13 hurricanes and six major hurricanes, with one – Hurricane Iota – attaining Category 5 on the Saffir-Simpson scale.

The season’s storms produced damage numbers in excess of US$51.14 billion dollars and in excess of 431 total fatalities. This season also featured a record 10 tropical cyclones that underwent rapid intensification, tying it with 1995. This unprecedented activity was fuelled by a La Niña that developed in the summer months of 2020.

The Cayman Islands National Weather Service has two main sources for seasonal hurricane prediction: the Colorado State University and National Oceanic and Atmospheric Administration (NOAA).

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The Colorado State University team, led by Philip Klotzbach and Michael Bell, provides updated prediction throughout the year, while NOAA’s representatives provide a forecast in May each year.

An average hurricane season produces around 12 named storms, six hurricanes and three major hurricanes.

The Colorado State team’s April 2021 forecast for the Atlantic Basin hurricane season calls for an above-average season with 17 named storms, eight hurricanes and four major hurricanes.

In terms of the factors that impact the number and strength of storms during the hurricane season, a scientist at the Colorado State said, “Current weak La Niña conditions may transition to neutral ENSO (meaning neither El Niño nor La Niña) by this summer/fall, but the odds of a significant El Niño seem unlikely. Sea surface temperatures averaged across the tropical Atlantic are currently near average, while subtropical Atlantic sea surface temperatures are warmer than normal.”

CLIMATOLOGY OF THE HURRICANE SEASON

To remind all, the hurricane season starts on 1 June and runs through to 30 November.

These dates are based upon long-term monthly numbers of tropical storms and hurricanes.

Despite these long-term numbers, it should be noted that a number of systems do, in fact, form outside the normal hurricane season. For example, Tropical Storm Alberto formed in May 2018 and Tropical Storm Arlene formed in April 2017.

During the season, there are usually low numbers of hurricanes in the first half of the season, leading the public to possibly question the accuracy of the forecast.

The peak of the hurricane season is considered to be around 11 September and is based on long-term numbers. The second half of the season tends to produce very powerful hurricanes, some of which form in the western Caribbean.

The three problems with these late-season storms forming in the western Caribbean include possible short warning times, erratic paths and potential of rapid intensification.

Examples of such storms include Hurricane Mitch 1998, Hurricane Michelle 2001 and Hurricane Paloma 2009.

Residents not aware of the late season climatology of the region may be caught preparing for a weak storm but get caught when a major storm hits. As a result, residents should always be prepared for the impact of a major storm, especially in the latter part of the season.

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