Bermuda Day Thunderstorms


AQUA MODIS imagery for the afternoon on the 24th, just after the squall line passed Bermuda. Parent extra-tropical low pressure center very wrapped up to the east of New Jersey.
AQUA MODIS imagery for the afternoon on the 24th, just after the squall line passed Bermuda (bottom-center). Parent extra-tropical low pressure center very wrapped up to the east of New Jersey/southeast of Cape Cod.

A very tightly wrapped extra-tropical storm along the Gulf Stream east of New Jersey and its associated upper tropospheric disturbance invigorated a pre-frontal trough near Bermuda. An outflow boundary crossed the island in the early afternoon with some thunder and squally showers (isolated unofficial gusts were near 35mph as the boundary came through). This outflow boundary formed when thunderstorms to our west created a shallow, near surface pool of rain-cooled air that then acted like a small scale cold front. However, those showers were in fact associated with a pre-frontal trough. That trough then lay oriented west-east to the near north of Bermuda as the parent low pressure center moved eastwards, further from the New Jersey coast.

Bermuda Weather Service Radar at about 12:33am this morning showing line of thunderstorms overhead oriented along the length of the island with heavy rain.
Bermuda Weather Service Radar at about 12:33am this morning showing line of thunderstorms overhead oriented along the length of the island with heavy rain.

By 9pm, showers and thunderstorms had redeveloped along the trough, and they lingered to the north of the island for about an hour before the cold front caught up to the pre-frontal trough and it began progressing southward – across Bermuda. This band of west-east oriented thunderstorms slowly slid southwards across the island bringing torrential rain, shifting, gusty winds, and frequent dangerous lightning (some buildings reportedly were struck). Thunderstorms then lasted into the wee hours of the 25th as they slowly cleared south of the island. Thunder and lightning remained visible to the south of the island until sunrise by which time the thunderstorms responsible moved far enough away.

Over an inch of rain fell from this system; officially 1.04″ at the airport, with unofficial reports across the island suggesting a widespread 1.00-1.50″. Much of the heavy rain (making for good tank water), with rainfall rates over 3.00″/hr at times, fell during low tide and that likely played a role in lack of flooding – that along with the recent dry spell. This follows April officially having less than 2″ and May warming up to near 80F (officially 79.9F) on the 23rd.

Fortunately, much of this inclement weather is clearing away from Bermuda leaving behind drier skies and less humid weather for the bulk of the Bermuda Day festivities on the 26th. See the Bermuda Weather Service for the latest official forecasts and advisories for Bermuda.

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