Dr. Masters co-founded wunderground in 1995. He flew with the NOAA Hurricane Hunters from 1986-1990. Co-blogging with him: Bob Henson, @bhensonweather
By: Dr. Jeff Masters , 2:04 PM GMT on September 12, 2011
Tropical Storm Maria continues to struggle with moderate wind shear of 15 - 20 knots that is preventing the storm from organizing. The center of circulation lies fully exposed to view this morning, with satellite loops showing that all of Maria's heavy thunderstorms lie to the east of Maria's center. Spiral bands from Maria are bringing heavy rains to the Virgin Islands and northern Lesser Antilles, as seen on long-range radar out of Puerto Rico and Martinique radar. Radar-estimated rainfall amounts of three inches have occurred in the Virgin Islands; 0.94" has fallen in St. Thomas, which experienced a wind gust of 39 mph at 9:14 am local time.
Maria's center has been tracking more to the west than the forecast has been calling for, but since the center is so far from the heaviest thunderstorms, I wouldn't be surprised to see the center reform more to the east or east-northeast later today. The models are in unanimous agreement that Maria should resume a more northwesterly motion later today, and turn to the north by Tuesday. The trough of low pressure that is bringing hostile wind shear to Maria is predicted to slowly weaken over the next few days, which may allow the storm to grow to Category 1 hurricane strength by Wednesday. Intensification will be hampered by the fact that Maria will be passing over the cold water wake left by Hurricane Katia, though. On Wednesday, Maria will be making its closest approach to Bermuda. If Maria does manage to organize into a hurricane, Bermuda could see an 8-hour period of sustained winds of 35 - 40 mph beginning near 2 pm local time on Wednesday. Most of the models show that Maria will brush or strike Newfoundland, Canada on Friday morning. Heavy rains will be a flooding threat to the west of where Maria passes, and wind damage from high winds of 50 - 60 mph will be a concern to the east of where the center goes.
Figure 1. Morning satellite image of Tropical Storm Maria.
Extratropical Storm Katia pounding Britain
Hurricane Katia brushed by Newfoundland, Canada on Saturday, and made the transition from a tropical system to a powerful extratropical storm. Extratropical Storm Katia maintained strong winds of 50 - 65 mph as it crossed the Atlantic, and is now lashing the northern British Isles with high winds and heavy rain. At 1 pm local time, the center of ex-Katia was over northern Scotland, and Malin Head, Ireland on the north coast of Ireland, was experiencing sustained winds of 49 mph. Winds in western Scotland were also high, with Aonach Mor recording sustained winds of 51 mph at 12:50 pm local time. The UK Met Office is warning that wind gusts up to 80 mph can be expected in Scotland today, as well as flooding rains of 2 - 4 inches. Ex-Katia's strong winds will likely cause significant tree damage and power failures across Northern Ireland and Scotland today.
Figure 2. Surface wind estimate from the Windsat satellite at 4:04 am EDT on Monday, September 12, 2011. The center of Extratropical Storm Katia is marked by an "L", and winds in excess of 50 knots (58 mph, purple triangles) were occurring to the southwest of the center, near the west coast of Ireland. Image credit: NOAA.
Britain's hurricane history
Hurricanes that transition to powerful extratropical storms hit the British Isles several times per decade, on average. In September 2006, two major hurricanes named Gordon and Helene transitioned to strong extratropical storms that hit the British Isles. Only once since accurate records began in 1851 has an actual hurricane with full tropical characteristics hit Europe. This happened on September 16, 1961, when Category 1 Hurricane Debbie hit northwestern Ireland. Wind gusts reached 106 mph at Ballykelly and 104 mph at Tiree and Snaefill, and coastal radio stations reported the airwaves were jammed with calls for help from small ships and fishing craft. Eleven people were killed and 50 injured in the storm. The only other tropical cyclone recorded to have hit Europe since 1851 was Hurricane Vince of 2005, which hit southern Spain as a tropical depression on October 11, 2005. Historical documents also suggest a hurricane hit Spain on October 29, 1842.
As reported by UK Met Office forecaster John Hammond in a post on the BBC 23 degrees blog, Britain has been affected at least eight times in the past twenty years by extratropical storms that were once tropical storms or hurricanes. The most recent one was Hurricane Bill of 2009, which hit Ireland on August 25 with sustained winds of 45 mph. Bill was a Category 4 hurricane northeast of the Lesser Antilles five days prior. In 2006, a record three extratropical storms that had once been tropical cyclones hit Britain:
Extratropical Storm Alberto, which had been a strong tropical storm that hit the Florida Panhandle, hit northern Ireland and Scotland as an extratropical storm with 35 mph winds.
Extratropical Storm Gordon hit Ireland on September 21, 2006, with sustained winds of 65 mph. Gordon brought record warm temperatures as tropical air pushed north across the UK, and also strong winds that brought down power lines in Northern Ireland. Wind gusts to 60 mph (97 km/h) occurred in the Isles of Scilly off the southwest coast, and 81 mph (130 km/h) on the mainland.
Extratropical Storm Helene hit Northwestern Ireland on September 27, 2006, with sustained winds of 45 mph.
Figure 3. Path of Hurricane Lili of 1996, which caused $420 million in damage to the U.K. as an extratropical storm.
Other post-tropical cyclones that have the U.K. in the past twenty years include Hurricanes Isaac and Leslie of 2000, Hurricane Karl of 1998, and Hurricane Lili of 1996. The most severe of these storms was Extratropical Storm Lili, which hit Ireland on October 28, 1996, with sustained winds of 65 mph. Lili caused $420 million in damage (2011 dollars) in the U.K. According to Wikipedia, Lili produced a 92 mph (148 km/h) gust at Swansea, South Wales, while bringing a four ft (1.20 m) storm surge that inundated the River Thames. In Somerset, 500 holiday cottages were severely damaged. A United States oil drilling platform, under tow in the North Sea, broke loose during the storm and nearly ran aground at Peterhead. On the Isle of Wight, a sailing boat was beached at Chale Bay; luckily all five occupants were rescued. It was the most damaging storm to have struck the United Kingdom since the Great Storm of 1987, which killed 22 and did $660 million in damage (1996 dollars.) However, Lili also broke a four-month drought over southwest England.
Elsewhere in the tropics
Several of the models predict the development of a tropical depression or strong tropical disturbance 4 - 5 days from now off the coast of Africa. The NOGAPS model is predicting the Western Caribbean could see the development of a strong tropical disturbance 6 - 7 days from now.
I'll have an update Tuesday morning.
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