May 2012 PWS Report

May 2012 was characterized by two extreme precipitation events. Although the temperature throughout the month was slightly below average, there were no powerful storms or cold fronts to note. However, a warming trend as we head towards the warmer summer months was evident throughout the month.

The first heavy rain event was on the 11th of May. Strong thunderstorms dumped heavy rains across Bermuda. During this 24 hour period between 1 and 3 inches of rain fell. Western parishes got more rain as a result of a batch of isolated showers that passed over that end of the island before the bulk of the rain moved in. Gusty winds were recorded, but no damage was observed as a result of these thunderstorms. Some minor flash flooding was seen in low lying areas (eg. around Mill Creek/Canal) as rainfall rates reached 5 inches an hour.

Bermuda (32N, 64W) trapped along a trough of convergence with low pressure to the west and high pressure to the east. A weakening Tropical Storm Alberto (30.5N, 77.9W) is a part of the low pressure in this satellite image. NOAA GOES East Satellite imagery May 21 2012 2115 UTC.

The next was a five day period from the 19th to the 24th of May. This event was dominated by a weather pattern that favored low pressure to our west and high pressure to our east. This meant that a moist southerly flow would develop with low level moisture originating in the Caribbean and upper level moisture originating in the Eastern Pacific. The low pressure to our east eventually spawned both of the month’s named storms. This deep tropical moisture was wrung out by the convergence created by the low to our east and high to our west bringing a solid two inches of rain across the island. This rain event was not as isolated – widespread moderate rain, mainly on the 22nd, dealt a second blow to the long term drought and eliminated the short term drought. Some patchy fog was recorded on the 24th in the wee hours of the morning (very cool stuff!), but this cleared out for the post-dawn morning hours, some isolated showers brought an additional half inch of rain to central parishes bringing their total up to 2.5inches. The 24th of May Bermuda Day holiday was not ruined, however, as these showers only lasted about an hour.

Although an almost unprecedented two Tropical cyclones developed over the Gulf Stream, neither of them warranted advisories for Bermuda. Tropical Storm Alberto peaked with 60mph winds and 998mb pressure, while Tropical Storm Beryl had max winds of 70mph and a min pressure of 992mb. The post-tropical remnants of Beryl brought strong wind gusts to Bermuda (20-25mph) and some isolated showers along its weak cold front.

May 2012 was the first month to end with above normal precipitation since August 2011, and it had some of the greatest 24hour rainfall totals in Spring since 2008 – very impressive for what is typically the driest month of the year.


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