Tuesday March 25th saw a weak low pressure move across Florida, then northeastwards over the Gulf Stream. At the same time, a weak low pressure moved eastwards out of the Ohio Valley and off the Mid-Atlantic coast. Atmospheric conditions over the Gulf Stream, east of the Mid-Atlantic states were prime for surface pressures to fall in that area. Both disturbances merged and, with very conducive atmospheric conditions, the resulting low rapidly strengthened. The low deepened from 1000mb Tuesday afternoon at 3pm Bermuda time, to 955mb at 3pm Wednesday afternoon; a staggering pressure drop of 45mb in 24hours. A non-tropical low pressure system deepening at a rate of 24mb/24hours is termed a “bomb” and this storm certainly fit that category. This storm brought a violent blizzard to Atlantic Canada and parts of coastal New England, including Cape Cod and Maine. Over a foot of snow with drifts over 3feet were reported in parts of Nova Scotia. Not to mention hurricane force winds observed, not only out over the Gulf of Maine and the North Atlantic, but also in some of the coastal and higher elevation locations of Maritime Canada. Peak gusts were over 115mph. It appears that these winds didn’t result in significant widespread damage or power outages because of their relatively isolated nature.
High pressure quickly slid off to the east of Bermuda on Tuesday, allowing southeasterly flow to develop. This southeasterly flow strengthened to Gale force by evening with intermittent light to moderate rains. A non-convective surface feature appears to have crossed the island around 10pm local time Tuesday night. This may have been associated with a surface warm front or trough, but that is unclear. As this feature approached, surface pressures fell 1-2mb in a ten minute period, and widespread gusts to storm force were observed. The airport recorded a gust to 63mph at this time, while unofficial reports indicate gusts between 65 and 70mph. These winds resulted in isolated power outages.
Unusual temperature patterns existed on Tuesday as cold high pressure retreated during the morning and strong southeasterly flow set up. Temperatures started in the mid-50s Tuesday morning, only rising to about 65F from daytime heating. After sunset, when the southeasterly flow was beginning to reach strong to near gale force, temperatures began to rise. They rose from 65F at sunset to 71F just after mid-night.
Wednesday morning saw another day of unusual temperature trends. A strong cold front passed in the morning, shifting southerly winds sharply to the west. Temperatures then fell through the day, staying in the mid 60s for much of the day and peaking in the low 70s before dawn. Scattered post frontal, cold air showers brought squally conditions with the general westerly gales to the island with the airport reporting peak gusts to 58mph. In the heaviest of these showers, rain-cooled air and cold air down-draughts dropped temperatures into the low-mid 50s overnight.
Gales quickly diminished overnight on Wednesday into Thursday as a significant high pressure shifted in overhead, but a dense stratocumulus deck kept skies mostly cloudy to overcast with a few light showers lingering. A cool northwesterly to northerly wind in addition to this cloud cover led to a high of only 61F at the airport, and while no record lows were broken, temperatures were 6-8F below average for this time of year – impressive as sea-surface temperatures, the great moderators of cool air flows to Bermuda were above normal before the storm.
Looking forward, southeasterly winds should continue the rebound back to/above normal temperatures for Sunday. This southeast wind, increasing to strong overnight Sunday into Monday, should also bring a return to high humidity, but generally fair skies becoming cloudier through the day. That increase in clouds is associated with a low pressure center moving slowly across Pennsylvania and into New England. A cold front associated with this low pressure should approach Bermuda overnight Sunday into Monday, and cross the island on Monday morning. Showers and thunderstorms are likely to be associated with this front on Monday morning. Strong southeasterly to southerly winds on Monday morning shift to the west as the front passes, remaining strong. Strong west to west-northwest winds Monday afternoon and overnight into Tuesday may briefly reach near-gale force with scattered, mainly post-frontal light showers.
This same low pressure system, slowly moving eastwards south of Atlantic Canada on Tuesday, then tracks slowly southeastwards on Wednesday through Thursday. This track keeps slowly diminishing west-northwesterly to northwesterly flow in place across Bermuda through to Friday. This persistent flow keeps temperatures below normal into the first few days of April. Cool air filtering in over Bermuda on this flow could also keep skies fairly cloudy and threaten isolated light showers at times.