Uncommon May Gale


Gales developed on Friday as a small low pressure passed just under 80 km to the north. This low was one of a series of small-scale low pressure systems that tracked from west to east along a quasi-stationary front near Bermuda last week.

Ahead of Friday’s low, that quasi-stationary front lifted northward across the island with patchy light rain showers on Thursday night. This was accompanied by an increase in temperatures and humidity as southwesterly winds strengthened early Friday morning. Southwesterly winds briefly increased to gale force (sustained >34 kts) with unofficial gusts over 45 kts reported at automated weather observing sites. Winds then dropped off slightly, veering through to northerly as the front moved across Bermuda from west.

GRAPH_PearlIsland_2017-05-12-1259-L
Graph of automated unofficial observations from Pearl Island sensors showing falling pressure and southwesterly winds increasing to gale force before 10am. Then winds drop off, veer to the north and temperature falls between 10am and 11am as the cold front passes. Northerly winds return to gale force after 11am as pressure rises. A similar wind trace was observed at Crescent and in official observations, however, the minimum in winds at Pearl Island was much more dramatic.

Cooler air then blew in as winds veered to the north on renewed gales behind the front. Storm force (>48 kts) gusts were recorded around the island, with a peak official gust of 49 kts at the airport, the second highest official gust observed in May since 1949*. High winds resulted in diverted flights (Royal Gazette/Bernews), delayed start to Relay for Life (Bernews), and several boat incidents (Bernews).

2017-05-12-1157_250km_sri
Bermuda Weather Service Radar at 8:57am local time as the small scale low was passing north of Bermuda. Much of the rainfall is confined to an east-west front about 80 km north of Bermuda, and southwest-northeast oriented cold front about 40 km south of Bermuda.

Very little rain fell from this system. Much of the shower activity was confined to the north of the island (along the front near the centre of the low), and south of the island (along the front). Pressure fell to 1000.7 hPa as the low passed the island, the lowest pressure observed in May since 2007**.

* Only 6th May 1978 had a higher gust at 50 kts, but the record is incomplete prior to 1996.
** This statistic is not recorded prior to August 2006.
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