Strong Storms, Now Cooler air in place


RGB Satellite imagery Friday February 14th 2014 after the cold front passed the island clearing its heavy rains to the east of Bermuda.
RGB Satellite imagery Friday February 14th 2014 after the cold front passed the island clearing its heavy rains to the east of Bermuda.
westatlantic-radar-2014-02-14-0103
Bermuda Weather Service radar February 14th at 1:03am local time showing discrete, potentially severe thunderstorms to the southeast of Bermuda and a line of thunderstorms to the west of Bermuda. This is hours before the heaviest rain fell leading to flash flooding.

A pre-frontal trough Thursday night led to some gusty showers with brief heavy downpours. However, the real rainfall came early Friday morning, along and just ahead of the cold front, thunderstorms containing very heavy rains crossed the island dumping between 2.50 and 3.75 inches of rain, the majority of which fell between 3:00am and 4:30am Friday morning.  This heavy rain resulted in localized flash flooding and even a landslide reported in the Palmetto Road area where work was being done to repair a retaining wall. Gusty winds from these thunderstorms reached peak gusts to 43kts (49mph) at the airport where 2.72″ of rainfall was observed.

Friday’s cold front cleared quickly to the east and south, and strong westerly winds behind the front on Friday morning quickly diminished to light or even calm by Friday night. The post-frontal airmass, clear skies, and light winds in place allowed temperatures to fall into the  upper 50s island wide for the first time this month in the pre-dawn hours of the 15th. Light and variable to calm winds at dawn, began to pick up and settle out of the southeast. These southeasterly winds signaled the return of more humid and warmer air. Temperatures recovered to the low-mid 70s with warm air being blown in on southeasterly winds. These winds increased to strong and veered more to the south by mid-day and southwest by evening.

100km_sri-radar-2014-02-15-1746
100km Bermuda Weather Service Radar around 6pm local time on February 15th showing an isolated discrete strong/severe thunderstorm scraping Bermuda to the south. Similarly structured thunderstorms were observed later, but further to the southeast.

The remains of Friday’s cold front were drawn northwards as a trough in this southerly flow. Strong to severe thunderstorms developed along and ahead of this trough as it was pulled northwards. A widespread area of isolated strong to severe thunderstorms moved in, some of these thunderstorms exhibited supercell and bow-echo representation on Bermuda Weather Service Radar. Isolated severe wind gusts and downpours were observed as some of these strong to severe thunderstorms scraped by the island. Much of the severe weather missed the island, but sustained winds of 45mph with a gust to 67mph was observed at the airport, likely associated with a bow echo feature that crossed the eastern parishes.  This significant weather was all associated with a pre-frontal trough that cleared away by 11pm, the cold front then passed around 1am Sunday morning with little fanfare. Although there were heavy downpours associated with Saturday’s strong and severe thunderstorms, they were moving very quickly and so precipitation totals were around a quarter or a third of an inch – a far cry from the extreme precipitation that fell Friday morning.

westatlantic-radar-2014-02-15-2203
Bermuda Weather Service Radar imagery around 10pm local time showing line segments of thunderstorms with embedded bow echo regions. This radar image is shortly after severe wind gusts were observed at the airport.

Strong to near gale force winds then took over for Sunday in the post-frontal airmass. Westerly winds were slow to decrease through the day as post-frontal troughs pushed through with light showers. Winds decreased to moderate by Monday night, and continued to veer through to the north. Today, light to moderate northerly winds veered east-southeasterly  and continue in the area as the day’s stratocumulus cloud regime begins to break up and shift northwards. It was this stratocumulus cloud deck and light to moderate northerly winds that kept today’s high in the mid-60s.

A ridge of high pressure is building to the south of Bermuda and should push northwards. This ridge maintains light/moderate southeasterly to southerly flow into Wednesday with warmer temperatures and clearer skies. However, a weak front approaches Thursday with a chance for showers, but right now it looks like the front will cross Bermuda. Moderate winds veer southwesterly ahead of the front Thursday morning and become light. These light winds become erratic as a col passes near Bermuda on Thursday. Winds should remain light and settle out of the west by Thursday evening. They remain light and may again become variable as the center of the ridge passes near Bermuda Thursday night into Friday morning. Winds then settle out of the South on Friday as another frontal system approaches.

Summary: mainly fair and unseasonably warm weather in place for the rest of the work week. An enhanced chance for showers on Thursday as a weak front approaches. Winds should remain light and become erratic  later this week as a col and then surface ridge pass nearby. Always follow the Bermuda Weather Service for the latest official forecast and warning products for Bermuda.

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