Tropical Storm in May? Uncommon but not Unheard Of

5 05 2019

Dale C. S. Destin |

The first tropical disturbance for the year has formed and is currently over the Western Atlantic, near the southeast United States. Although this system is unlikely to form, it is not unheard of for tropical storms to develop in May, but it is relatively uncommon.

1st #TropicalDisturbance of the year (circled). The bright colours popping up are lightning flashes. pic.twitter.com/gQAheDc9iR

— 268Weather (@268Weather) May 1, 2019

Looking back at the history, there have been 26 tropical storms in May, 4 of which became hurricanes – all category ones. This means, on average, one tropical storm forms every 6 to 7 years, based on data for the period 1981-2010, upon which the current climate is based.

All Tropical Storms in May on Record, 1851 to 2018

All May Tropical Storms, on Record – 1851 to 2018

The probability of a tropical storm forming in May is 15% (a slight chance), which means storms seldom form in May. The last time this happened was back in 2016 – Tropical Storm Bonnie.

Hurricanes in May are even more uncommon, if not rare. The probability of one forming in May is less than 3%, based on the full history – 1851 to 2018. This means there is a hurricane in May, on average, once every 42 years – once in a generation plus. The last one was Hurricane Alma of 1970.

What do you think? When a named storm (tropical storm or hurricane) forms in May, what kind of hurricane season normally follows?

— 268Weather (@268Weather) May 1, 2019

One may be tempted to think that a tropical storm in May is an omen for an active (above normal) hurricane season. In a (small) poll done by me on twitter, 61% of persons said that a storm in May means an active or hyperactive season; however, this is false. The record shows the following w.r.t. seasons whenever there has been a storm in May:

3 hyperactive;
4 active (above Normal);
11 normal and
5 quiet (below normal).

In other words, whenever there was a storm in May:

4% of the time the seasons were hyperactive;
17% were active;
48% were normal and
22% were quiet.

Hence, a storm in May seems to portend a normal hurricane season, as opposed to an active or hyperactive season. So, we may, perhaps, want to wish for a storm in May.

With all the talk about climate change and tropical cyclones, one may be tempted to think that we are having more storms in May than before. However, the record does not bear that out. In the 38 years from 1981 to 2018, there have been nine tropical storms, no hurricane. By comparison, during the previous 38 years, there were eight tropical storms, two of which became hurricanes.

While tropical storms are not unheard of for the Atlantic Basin, they are unheard of for our neck of the woods – Antigua and Barbuda. We have never been impacted by a tropical cyclone (tropical depression, tropical storm or hurricane) in May.

The fortune of never having a tropical cyclone in May extends to the rest of the Eastern Caribbean. As a matter of fact, none has ever formed east of Hispaniola. Further, no hurricane has ever impacted/affected any Caribbean island in May. Clearly May is not a month to be worried about tropical storms.

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