Tropical Storms in May Mean Nothing

15 05 2020

Dale C. S. Destin |

The first tropical or subtropical storm for the pre-hurricane season is about to form in the Bahamas. Some think that this is a harbinger (sign) for the upcoming hurricane season – June 1 to November 30, but is it?

Tropical disturbance AL90 across the Bahamas with an 80% chance of becoming Tropical Storm Arthur within 48 hours.

To the “naked eyes”, it is understood why some may take a storm forming in May as a sign of bad news for the upcoming hurricane season; however, the numbers don’t agree.

The numbers say that it usually means nothing in terms of the overall activity of the upcoming season. According to NOAA, there have been 29 named storms in May, spread over 27 seasons from 1842 to 2019. Of the 27 seasons, using NOAA’s definitions, nine were above normal (active or hyperactive), 11 were near normal and 7 were below normal (inactive or quiet).

Overall, most seasons with a storm in May, are near normal – 11 times of 27 – 41%. However, from a statistical standpoint, there are no significant differences between above, near or below normal seasons, when there is a storm in May. Hence, a tropical storm forming in the month has no bearing on the activity of the upcoming hurricane season.

Of the 27 seasons with May storms, 9 or 33% was active or above normal; 11 or 41% was normal and 7 or 26% was quiet or inactive

Notwithstanding the above, this hurricane season is expected to be above normal or likely hyperactive – well above normal, see my latest forecast. Clearly, this has nothing to do with the expected formation of Tropical Storm Arthur over the Bahamas.

Further on the tropical cyclone climatology on May, of the 29 named storms to have formed in the month, 5 became hurricanes with none ever becoming a major hurricane. The strongest tropical cyclone of the month occurred in 1863 – a Category 2 unnamed cyclone.

The only Cat 2 May Hurricane on record – Unnamed Hurricane – 1863

On average, there is one storm forming in May every 7-8 years. However, there have been a storm in May of the last 2 years and 6 in the last 10 years. Twice, two storms formed in May of the same season – 2012 and 1887, the most of any. So much for averages, right!

The Eastern Caribbean has never been impacted by a tropical cyclone in May, “knock wood”, based on available record dating back to 1842.

Storms forming in this part of the region in May are not unusual. Of the 29 May storms, 28% have formed or traverse within 300 miles of Nassau, Bahamas.

Unfortunately for the Bahamas, this year they are still recovering from Super Category 5 Hurricane Dorian of September 2019, which levelled much of Northwest Bahamas. You may say that they can’t “catch a break”, as they are about to deal with potentially strong storm-force winds and flooding rainfall, in addition to dealing with the COVID-19 Pandemic.

Possible tracks of what is expected to become Tropical Storm Arthur in 48 hours

May storms mean nothing in terms of the overall activity of the hurricane season; however, they mean a lot with respect to where they impact. Let us be prepared regardless of omens or forecasts for the season – it only takes one hurricane to ruin your year or life.

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