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Distance travelled ~ 771'143'200 km

(Here Dr. Jeff Masters, Director of Meteorology, wunderground.com explores 2011's Atlantic Hurricane season. His previous post for 23 Degrees provided us with a detailed roundup of Maria, Nate and Katia's developments.)

The Atlantic is nearing its end, with Tropical Storm , near Mexico's Yucatan Peninsula, likely to be one of last storms of the season. Atlantic hurricane activity peaks near September 10, and drops dramatically during the last half of October. It's been a very strange year for hurricanes in the Atlantic. There have been a near-record number of named storms--seventeen--making 2011 the 7th busiest year for tropical storms since record keeping began in 1851. However, only six of those storms--35%--have intensified to hurricane strength. In a typical year, 55 - 60% of all tropical storms make it to hurricane strength. A rare combination of near-record warm ocean temperatures but unusually dry, stable air over the Atlantic is no doubt partially responsible for this very unusual occurrence. Another unusual feature of this hurricane season is that relatively few storms hit the U.S. During the 15-year active hurricane period from 1995 - 2009, 33% of all named storms in the Atlantic hit the U.S., and 30% of all Atlantic hurricanes hit the U.S. at hurricane strength. Based on 1995 - 2009 levels of activity, the U.S. should been hit by six named storms, four of those being hurricanes, and two being intense hurricanes. So far, 2011 has seen less than half that level of landfall activity. Two tropical storms and one hurricane have hit the U.S. this year: , which hit Texas with 50 mph winds, , which hit Louisiana with 60 mph winds, and , which hit North Carolina with 80 mph winds. This is the second consecutive year that the U.S. has benefited from favorable steering currents that have steered most of the storms out to sea. During 2010, only one tropical storm hit the U.S., despite a season with the 3rd highest number of named storms, nineteen. If 2011 finishes without a major Category 3 or stronger hurricane hitting the U.S.--which is likely--it will mark the first six-year period without a major hurricane strike on the U.S. since record keeping began in 1851. The last major hurricane to hit the U.S. was Category 3 Hurricane Wilma of October 2005.

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The strongest hurricane of 2011 was , which peaked as a Category 4 hurricane with 140 mph winds and a central pressure of 940 mb on October 2 just northeast of Bermuda. Ophelia hit Southeast Newfoundland as a tropical storm with 70 mph winds on October 3, but caused little damage. The longest-lived storm was , which lasted 15 days from September 24 to October 8. The most damaging was , which caused at least $7 billion in damage from North Carolina to New England. Irene was also the deadliest storm of 2011, with 55 deaths in the Caribbean and U.S. being blamed on the storm.

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Figure 3. Hurricane Irene's storm surge and winds carved two new channels through Pea Island on North Carolina's Outer Banks. This cut, near the town of Rodanthe, is the smaller of the two cuts, and severed Highway 12 connecting the Outer Banks to the mainland.

What do you think of this year's season?

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Distance travelled ~ 765'461'600 km

Over the Americas:

• A large area of low pressure will track eastwards through the Bering Sea and Alaska towards Nunavut in Canada from Sunday through to Thursday, bringing very wet and windy conditions, particularly to the more populated southern/western seaboard of Alaska and Canada.

• Hurricane Rina, Category two, is moving slowly at 3mph northwest over the western Caribbean - Belize, the east coast of the Yucatan Peninsula and adjacent Islands should monitor the progress of Rina. A hurricane watch is in effect for the east coast of the Yucatan Peninsula from north of Punta Gruesa to Cancun.

According to the National Hurricane Centre additional strengthening seems likely until increasing south-southwesterly shear halts the intensification process which is expected to occur in about 48 hours.

• A second area moving into the eastern Caribbean into the new working week, tracking eastwards past Venezuela before likely losing its impetus by Thursday.

• A deep area of low pressure is forecast to bring very heavy rain and strong winds to Uruguay and southern Brazil during the middle of the week.

Across Europe:

• Systems of low pressure near the UK will bring unseasonably wet and windy weather to Morocco, Iberia, Biscay and the UK at the start of the week.

• Further heavy rain from a second low pressure system is expected to affect Iberia midweek.

• High pressure is expected to dominate the weather across eastern Europe, bringing increasingly cool conditions to the Black Sea and Caucasus.

Across Asia:

• Cool and windy conditions should affect northeastern China at the start of the week. Moving westwards into Vietnam and Laos over the next few days, bringing further heavy rain to these regions.

Across Australasia:

• Significantly warmer and wetter than average over New South Wales and Victoria at the start of the week, with heavy rain and strong winds later affecting the South Island of New Zealand during Monday.

• Very heavy rain is likely to push into Western Australia around Perth from the Indian Ocean around midweek.

Across Africa:

• Becoming warm or very warm for the time of year over southeastern Africa, particularly Mozambique and Madagascar, whilst in contrast Namibia and the Cape region of South Africa should see cooler than average weather.

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Distance travelled ~ 727'298'400 km

After a period of record-breaking settled weather last week, most of the UK saw a return to normal autumn conditions by Tuesday. A band of cloud spread across most of England and Wales, and showers continued in Scotland and Northern Ireland.

Wednesday and Thursday saw strong northwesterly winds for many, reaching gale force on higher ground in the north. On Thursday a yellow warning was in place for gusts of up to 65mph for parts of the North West and Northern Ireland, with winds in excess of 40mph recorded widely. The strongest gust at low levels was 66mph at Machrihanish in Scotland.

Temperatures fell compared to last week but were still above average in many areas for October, with a high of 22.1 °C in Bridlington on Wednesday. Although on Friday it was a chilly start for many, with temperatures falling into single figures and a low of -1.5 °C at Cairngorm in Scotland.

Elsewhere in the world, Winnipeg in America has also been experiencing warm autumn weather, with temperatures 18 °C above what is seasonally normal. It reached 31 C on Thursday, the hottest October day in Winnipeg since records began.

Several days of heavy rain in central Algeria have caused the deaths of eight people and widespread damage to roads and bridges. There has also been heavy rain in Haikou, China, where 17,000 people were evacuated after days of torrential rain raised the level of the Nandu river higher than the warning line.

One man has been killed and 12 injured in a massive pile-up after a dust-storm rolled across an interstate in Arizona. The collision on Interstate 10 near Picacho - midway between Phoenix and Tucson - involved 16 vehicles.

In Australia, almost 11,000 homes are without power after severe thunderstorms battered Queensland. However, damage from flooding has been minimal, with only 22 calls made to the State Emergency Service for leaking roofs.

Severe weather watch: The week ahead

Across Europe:

• Unsettled conditions are expected to continue to affect some northern parts of Europe through the start of the week.

• Warm and quiet conditions are expected to return to many areas from midweek as high pressure builds once again across Europe.

• The former Hurricane Philippe is set to head well north across the Atlantic, bringing gales and heavy rain to Iceland and East Greenland. In so doing, Philippe will give the UK a wide berth and will have no direct weather impact here.

Over the Americas:

• In the eastern Pacific Hurricane Jova and Tropical Storm Irwin are both moving towards Mexico. Jova is a Saffir-Simpson Category 3 Hurricane moving East (winds ~120 mph) and is expected to make landfall somewhere near Manzanillo on Tuesday.

Irwin is forecast to approach the west coast of Mexico on Thursday or Friday. Maximum sustained winds 35knots; 40mph moving east at 7mph.

Across Asia:

• There are unsettled conditions to the east of the Philippines at the moment and this may develop into a typhoon this week.

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Distance travelled ~ 649'203'200 km

(After almost getting killed flying into hurricane Hugo as a flight meteorologist for Hurricane Hunters, Dr. Jeff Masters left to pursue a Ph.D in air pollution meteorology from the University of Michigan. While working on his Ph.D he cofounded the very popular weather internet service 'The Weather Underground'. Here he shares his thoughts on the current tropical storm developments, just as the 23 Degrees team touches down in Mexico to film Nate.)

Tropical Storm is pounding the Lesser Antilles Islands with heavy rains and strong gusty winds. Maria's 45 mph winds are expected to steadily increase for the next five days as the storm takes advantage of warm ocean temperatures near 29.5°C and light winds aloft that put little shear on the storm's core. By Monday, Maria is expected to be a Category 1 hurricane, and may intensify to a Category 3 hurricane with 115 mph winds by Wednesday. Maria is headed northwest at 15 mph, and will pass through the Virgin Islands and skirt the eastern side of Puerto Rico on Saturday. The storm is expected to dump 100 to 200 mm of rain on the islands, with isolated amounts as high as 250 mm. Maria will turn to the north early next week and miss the U.S., but may be a threat to Canada late in the week.

A Hurricane Watch has been posted along the Mexican coast from Tampico to
Veracruz for the arrival of . Nate is nearly stationary in the Bay of Campeche, but is expected to move steadily westwards on Saturday and Sunday, and make landfall on Sunday as a strong tropical storm with 70 mph winds between Tampico and Veracruz. The primary danger from Nate will be heavy rains; 100 - 150 mm of rain is expected in coastal Mexico, with isolated amounts as high as 300 mm. Unfortunately, Nate will be too far south to being
rains to Texas, which is enduring its worst drought in recorded history.

Figure 1. True-color MODIS image of Tropical Storm Nate taken at 12:45 pm EDT Friday, September 9, 2011. At the time, Nate was a tropical storm with 50 mph winds. Image credit:

Hurricane is a few hundred kilometers south of Newfoundland, Canada, and is accelerating east-northeastward towards the open Atlantic. The hurricane is expected to pass over much colder waters of 18°C on Saturday afternoon. A hurricane cannot survive in waters less than about 25°C, and the cold waters will force Katia to transition into a powerful extratropical storm. Extratropical Storm Katia will continue east-northeastward towards Europe, and on Monday, the storm will pass very close to northern British Isles. The offshore waters of Northern Ireland and Western Scotland can expect storm-force winds of 50 - 65 mph as Katia roars past to the north. 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 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.

Figure 2. Image of Hurricane Katia taken from the International Space Station at 15:00 GMT September 9, 2011, by astronaut . At the time, Katia was a Category 1 hurricane with 85 mph winds. Long Island, New York is visible
at the lower left.

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Distance travelled ~ 647'488'000 km

Hurricane Katia, currently in the western Atlantic is set to steam due east towards the UK and is expected to . With it will come the risk of severe gales and heavy rain to parts of the UK. The strength and depth of this September storm is quite unusual, but similar storms that originated as hurricanes have affected the UK in the last 20 years several times.

Hurricane Bill - 2009

You only have to look back as far as 2009 to find a storm that crossed the Atlantic. Hurricane Bill formed on August 15th and reached the UK as a post tropical storm on August 25th, bringing severe gales and heavy rain two days after being downgraded from a hurricane to a tropical storm.

Hurricane Alberto, Gordon and Helene - 2006

In 2006, three post tropical storms reached the UK. Alberto, Gordon and Helene all brought wet and windy weather to the UK. Alberto combined with a cold front to the west of the UK whilst Gordon brought record warm temperatures as tropical air pushed north across the UK, but also strong winds that brought down power lines in Northern Ireland.

Hurricane Isaac and Leslie - 2000

These two hurricanes both affected the British Isles in the year 2000.

Hurricane Karl - 1998

Hurricane Karl made its way to southern Britain in 1998.

Hurricane Lili - 1996

Perhaps the most similar storm to Katia was in 1996 when the remains of hurricane Lili pushed across the UK just one day after being downgraded from a hurricane. The post tropical storm ran across Britain on 28th and 29th October. The storm brought gusts in excess of 90 mph, bringing widespread impacts across the UK and causing significant disruption.

Hurricane Katia - 2011

Katia is currently a category one hurricane off the east coast of the US and will run across the Atlantic through the weekend bringing the risk of severe gales and storm force winds in places later on Sunday and through Monday.

Although it is expected to be windy everywhere, it is uncertain as to exactly which parts of the country will see the very strongest winds and therefore you should stay up to date with .

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