2012 In Review


Winter 2011-2012 was much more benign than the previous few winters that were marked by multiple vicious winter storms that brought hurricane force winds to the island. In fact, none of the winter storms this season did that.

January saw three storms that increased winds to gale force with the most powerful of them early in the month. The relative lack of strong storms meant there were no record lows to report for this month and precipitation was notably below average. February saw only two winter storms that could have produced some severe thunderstorms but they did not affect the islands. The storms were well spaced through the month and again temperatures were very near normal with below normal precipitation.

March changed this pattern; after a strong storm early in the month, a blocking ridge of high pressure built in over the United States East Coast and the Western Atlantic. Temperatures stayed slightly above average with little precipitation for three weeks in the middle of the month as high pressure dominated. However, the ridge began to break down at the end of the month with two moderate strength winter storms. March 2012 ended as the driest March on record at the Bermuda Weather Service with only 0.79″ of rain recorded.

Record April Winter StormApril began with the most powerful winter storm of the year. Gusts reached 66mph with small hail and a record low of 50.2F being reported at the Bermuda Weather Service as this storm pushed through. Two weaker storm systems came later in April, but they weren’t too noteworthy with little precipitation and gales.

Bermuda Weather Service Radar image of the mesoscale convective complex associated with the disturbance exiting the island, headed northeast. At the time gales were just beginning to be observed at the Bermuda Weather Service. (June 17th 2012 3:23pm)
Bermuda Weather Service Radar image of the mesoscale convective complex associated with the disturbance exiting the island, headed northeast. At the time gales were just beginning to be observed at the Bermuda Weather Service. (June 17th 2012 3:23pm)

May and June were characterized by some notable heavy rain events that led to some localized flash flooding. One such event in June dumped over two and a half inches of rain in a few hours during evening rush hour leading to localized flash flooding and causing traffic to slow to a crawl. Tropical moisture interacting with the same stalled frontal system that produced the flash flooding allowed a wave of low pressure to gain tropical characteristics and begin to transition into a sub-tropical disturbance. It was still associated with frontal boundaries as it crossed Bermuda from Southwest to Northeast, but it was powerful enough to bring gale force winds with storm force gusts for 6 hours, winds peaked at 45mph with a peak gust of 64mph. This feature was largely under-forecast or missed entirely, probably because of sparse observations in the Atlantic. It later evolved into Hurricane Chris in the open north Atlantic where it transitioned back to an extra-tropical storm. The post-tropical remnants of tropical storm Debby passed to the north of Bermuda towards the end of June bringing strong westerly winds and some showers.

July’s weather was fairly benign, being dominated by the Bermuda-Azores ridge, although this pattern was interrupted towards the end of the month when a three day period of strong thunderstorms associated with a stationary front produced squally weather, dangerous cloud to ground lightning and dumped the majority of the month’s precipitation. After that unsettled weather cleared out Bermuda went back under the influence of high pressure into early August.

The influence of the Bermuda-Azores high relaxed mid-August to allow for a heavy rain event in which thunderstorms let around two inches of rain accumulate – about half the month’s precipitation. The rest of the month was plagued by intermittent rain showers and thunderstorms because of the tropical moisture that flowed in from the south around the western side of the Bermuda-Azores ridge.

Bermuda Weather Service Radar of Tropical Storm Leslie at its closest approach to Bermuda - MAX Radar range to capture size of storm. September 9th 2012 (5:21pm local time)
Bermuda Weather Service Radar of Tropical Storm Leslie at its closest approach to Bermuda – MAX Radar range to capture size of storm. September 9th 2012 (5:21pm local time)

September was marked by the slow passage of Tropical Storm Leslie, the storm, initially forecast to become a major hurricane, meandered to the south of the island for days – upwelling cooler waters and weakening itself. Its large size contributed to dry air entrainment that ultimately limited its strength for its passage to the east of Bermuda. However because it was such a large storm and it was moving so slowly over four inches of rain fell in one day leading to localized flooding at high tide. Winds likely reached the strongest the storm had to offer on its weak side with peak gusts to 55mph. Notably, the upwelling from the storm dropped sea surface temperatures by about 6F – they were running about 5F above average before the storm’s passage. The remainder of September was fairly lax in Bermuda with a few moderate rain events near the end of the month.

Another burst of tropical activity arrived in October, however this time, origins were found in the Caribbean rather than the central Atlantic. Hurricane Rafael passed threateningly to the east of Bermuda with rainfall amounts over two inches and peak gusts reaching 52mph on the 16th. Much of the month remained quiet until the end of the month when Hurricane Sandy pulled out of the Caribbean and then the Bahamas and transformed into a massive storm system. Tropical Storm conditions were felt particularly in the western parishes and higher elevations of Bermuda, squally showers brought an official gust to 58mph and a report of a tornado in Somerset, Sandy’s parish. The hurricane’s impacts lasted four days in Bermuda as the center of the storm moved northward between Bermuda and the United States East Coast for an unusual landfall in New Jersey.

Unsettled weather remained in place post- hurricane Sandy as a lingering trough of low pressure dominated the local weather. A trace of more of precipitation fell for 27/30 days in November leaving the month above normal in precipitation. A wave of low pressure passed the island nearing the end of the month allowing for the first winter storm gale event of the 2012-2012 season as wind gusts reached 48mph on the 23rd.

The meteogram from Commissioner's Point showing the passage of the severe squall line on December 30th. Gusts neared hurricane force.
The meteogram from Commissioner’s Point (a Bermuda Weather Service ASOS at 262ft to indicate conditions on hilltops) showing the passage of the severe squall line around 8:15am on December 30th. Gusts exceeded 60kts or about 70mph.

Mainly settled weather persisted for the first two thirds of December with no serious winter storms or rain events until the 18th when a complex system brought strong thunderstorms and persistent gales to the island. These gales lasted until the morning of the 22nd. Another winter storm passed on the 27th and into the 28th but it was not very noteworthy. Finally to end the month and the year a sharp cold front passed in the morning of the 30th with a severe squall line that produced gusts nearing hurricane force in the higher elevations of Bermuda and up to 60mph at the Bermuda Weather Service. Behind the front light rain transitioned into cold air convective showers that threatened small hail, and were accompanied by gales that quickly calmed as a transient ridge built in for New-Year’s eve and day. December ended well below normal in terms of precipitation, but near to slightly below normal in terms of air temperature.

Drought continued into 2012 with an annual total precipitation amount of 49.27″ officially recorded at TXKF, the Bermuda Weather Service. According to averages from 1981-2010, the mean annual precipitation is 58.66″. This puts Bermuda at a deficit of 9.39″ in 2012. That on top of 2011’s large precipitation deficit amounts to over 24″ of rain below normal in two years. The dry spring and early summer caused worrying agricultural problems as crops withered and were abandoned, and despite above normal precipitation in Summer months, much of it fell at once and didn’t soak into the ground efficiently. If this trend of below normal precipitation continues, we could be dealing with serious hydrological impacts in the near future.

NASA'a MODIS imagery captures Bermuda between cloud decks in early December.
NASA’a MODIS imagery captures Bermuda between cloud decks in early December.

Bermuda Weather Service observations show that 2012 was near normal in terms of air temperatures. According to averages from 1981-2010, the mean annual temperature in Bermuda is 72.3F, 2012 recorded 72.0F. Meanwhile, sea surface temperatures in Bermuda were above normal – averages calculated from 1949-1992 show that the mean annual sea surface temperature is 73.1F, the mean annual sea surface temperature in Bermuda was 74.2F – continuing the trend of above normal sea surface temperatures.

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s