A slow moving frontal system moved off the US East Coast and made its way towards Bermuda. Southerly winds ahead of the system brought warm humid air from the Caribbean and Southwestern Atlantic into the Bermuda region. A pre-frontal trough of low pressure started the rain showers in the morning of May 11th.
These earlier showers largely tracked over the western third of Bermuda, only small totals were observed in the central and eastern thirds. However, where these showers and thunderstorms did cross the island, they produced gusty winds and heavy downpours at rainfall rates of over three inches an hour.
The thunderstorms evolved through the day from being scattered to being in bands and squall lines. Most of the organized thunderstorm activity occurred as they passed over the island prompting a last minute Severe Weather Watch from the Bermuda Weather Service. There were no reports of severe weather, but gusts to gale force were observed in and around these squall lines.
As the afternoon’s high tide (around 1:45pm) began to ebb, most of the heavy rain fell. This allowed for low lying areas to experience flash flood-type conditions. As rainfall rates of up to five inches an hour were observed across the island with the slow moving thunderstorms. Areas affected by these floods typically flood during heavy rain events and so they were not unprecedented – no property damage was reported.
The rain cleared away by 7pm, however the front didn’t fully pass until the pre-dawn hours on the 12th. The front was weak and there was little change in temperature although the dewpoint took a big hit – dropping from the upper 60s to the low 50s.
Just to give this event some perspective; the daily precipitation totals on May 11th were the most significant since October of 2011, and the greatest daily totals in May since 2008.
Below are some rainfall totals taken from around the island;
|George’s Bay, Sandy’s||3.02″|
|Moore’s Lane, Pembroke||2.25″|
|Bermuda Weather Service||1.68″|
|Gilbert Hill, Smith’s||1.43″|
|Chaingate Hill (Me), Devonshire||1.42″|
|Knapton Hill, Smith’s||1.41″|