It's been a very strange year for the 2011 Atlantic hurricane season

    Distance travelled ~ 771'143'200 km

    (Here Dr. Jeff Masters, Director of Meteorology, 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 hurricane season of 2011 is nearing its end, with Tropical Storm Rina, 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: Tropical Storm Don, which hit Texas with 50 mph winds, Tropical Storm Lee, which hit Louisiana with 60 mph winds, and Hurricane Irene, 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.


    tracks of atlantic storms 2011

    Figure 1. Tracks and intensities of the seventeen named Atlantic storms of 2011

    The strongest hurricane of 2011 was Hurricane Ophelia, 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 Hurricane Philippe, which lasted 15 days from September 24 to October 8. The most damaging was Hurricane Irene, 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.

    hurricane irene as seen by nasa

    Figure 2. Hurricane Irene as seen by NASA's Aqua satellite at 18:15 UTC on August 24, 2011. At the time, Irene was a Category 3 hurricane with 120 mph winds over the Turks and Caicos Islands.


    two new channels carved by hurricane irene

    Image credit Western Carolina University

    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?



    Day 298 Severe weather watch: Cat 2 hurricane Rina intensifying

    Post categories:

    Dave Britton – Met Office | 12:30 PM, Tuesday, 25 October 2011

    Distance travelled ~ 765'461'600 km

    GOES 13 IR hurricane Rina

    Image courtesy of Naval Research Laboratory

    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:

    surface pressure forecast 25 oct

    • 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.

    Day 272: Typhoon Nesat in pictures

    Post categories:

    Aira Idris Aira Idris | 12:30 PM, Thursday, 29 September 2011

    Distance travelled ~ 698'568'800 km

    "These pictures were taken on the Ocampo Street in Malate, Manila Philippines beside Rizal Stadium" by Abby Thompson.
    vehicles left at a standstill in the flooding

    iwitness image captured by Abby Thompson

    heavy rain after typhoon nesat

    iwitness image captured by Abby Thompson, Philippines

    flooding in philippine

    iwitness image captured by Abby Thompson, Philippines

    vehicles struggle in the flooded street

    iwitness image captured by Abby Thompson, Philippines

    Nesat hit China earlier today and continues west:

    satellite image of nesat

    After Typhoon Nesat made landfall near Casiguran on the east coast of the island of Luzon in the Philippines 27 September, earlier today it made landfall in the northeastern part of Hainan island, China. It is moving west towards the far north of Vietnam, where it is predicted to make landfall within the next 12 hours. Nesat is weakening and likely to be categorised as a tropical storm soon.

    UK and World weather report: Typhoon Talas worst to hit Japan since 2004

    Dave Britton – Met Office | 17:30 PM, Monday, 12 September 2011

    Distance travelled ~ 655'367'200 km

    Last week brought typically varied conditions over the UK and while around the world tropical cyclones continued to dominate the headlines.

    It was unsettled across many parts of the UK last week. In a theme that would be repeated later in the week strong winds caused some disruption on Tuesday as an Atlantic depression crossed northern Scotland. Winds reached 80 miles per hour at the Needles on the Isle of Wight as ferries were cancelled and trees uprooted in Dorset, while over 80 mm of rain fell in Snowdonia.

    From midweek temperatures started to rise in eastern areas as warm air was drawn north from the continent. Highs of 24.8 Celsius were recorded at Wainfleet in Lincolnshire on Friday and 25.0 Celsuis at Leconfield, North Humberside and Weyborne in north Norfolk on Saturday.

    The wind started to pick up once again on Sunday with gales developing across Scotland and cloud and rain spread from the Atlantic. This was the pre-cursor to today's particularly stormy weather as a deep area of low pressure which contained post-tropical storm Katia brought gales and heavy rain to parts of the UK. The strongest winds were recorded in exposed areas of Northern Ireland, Southern Scotland, North Wales and parts of Northern England with gusts of 76 miles per hour at Malin Head and 73 miles per hour in Glasgow.

    Across the world tropical cyclones dominated the weather last week - Typhoon Talas struck the west of Japan early in the week, Tropical Depression Kulpa gave heavy rain and flooding over southern South Korea. Tropical Storm Lee drenched New York leading to complete loss of a days play at the US Open Tennis, Tropical Storm Maria passed by the islands of the northeast Carribean, Tropical Storm Nate affected the southwest of the Gulf of Mexico leading to the closure of Mexico's two main crude oil export ports.

    satellite image typhoon talas

    Typhoon Talas nears the southern islands of Japan in this NASA MODIS image from September 2, 2011

    Typhoon Talas was the most destructive typhoon to hit Japan since 2004. The typhoon swept through the west of the country on Sunday, dumping heavy rain and bringing winds of up to 68 miles per hour. Entire villages have been flooded, with bridges and houses destroyed.

    Tropical Storm Lee caused catastrophic flooding on the US coast, flooding streets, homes and businesses, reportedly leaving eight people dead and causing more than 130,000 people to be moved for their own safety. The storm struck Maryland to New England and dropped up to a foot of rain outside Harrisburg, Pennsylvania, which declared a state of emergency. Eight feet of water covered the river towns of Tunkhannock and Shickshinney. Elsewhere, the strong winds spread wildfires that destroyed homes and killed two people in Texas.

    What's in a name?

    Post categories:

    Peter Gibbs Peter Gibbs | 13:00 PM, Friday, 9 September 2011

    Distance travelled ~ 647'166'400 km

    (Peter Gibbs is a BBC weather forecaster and a regular blogger for 23 Degrees. With all the current Atlantic hurricane activity, here Peter tackles some of the questions flying around as hurricane Katia makes it's way to the UK.)

    "Do we get hurricanes in the UK?"

    No, it's not possible.

    "But what about the 1987 storm, wasn't that a hurricane?"

    Well, it did have hurricane force winds, which was why it knocked down 15 million trees, but it wasn't a hurricane.

    "How does that work, then?"

    I've lost count of the number of times that I've had that conversation during my career, but it's a reasonable question and one that's worth exploring during this very active Atlantic hurricane season.

    interactive forecast track cone katia

    Katia moving toward the northeast over the open atlantic

    hurricane katia 4 day forecast cone and track

    Weakening is indicated since the hurricane is already reaching cooler waters and Katia is forecast to become post-tropical in about 36 hours.

    Hurricanes are creatures of the tropics, they need the warmth and humidity of tropical seas to develop and survive. The core of the storm consists entirely of warm air and it's the release of latent heat as this air rises and condenses into clouds which gives the hurricane its power. It's a bit like a pan of water coming to the boil as you apply heat from below.

    Once formed, a hurricane moves through the surrounding atmosphere like a cork floating down a stream, becoming almost a separate entity. The strongest winds form in the lowest layers of the storm, close to the storm's centre just outside the eye.

    Move into temperate latitudes and weather works differently. Extratropical storms (more commonly known as mid-latitude depressions) form over much colder waters and get their energy instead from the contrast between masses of warm and cold air. The bigger the contrast, the stronger the storm. Cold air makes up the core, digging under the warmer air mass and lifting it until it forms clouds and rain along a front.

    The storm becomes an integral part of the atmospheric circulation, like an eddy in a river. Strongest winds are found high up, in the form of the jetstream, at around 30,000ft while the strongest surface winds tend to occur at some distance from the storm's centre and are spread out over an elongated area. All very different to a hurricane.

    Where it gets messy is when a hurricane heads out of the tropics and into higher, temperate latitudes. It goes through an identity crisis as the supply of warmth from below is cut off and cold air is drawn into the circulation, eventually emerging as an extratropical storm after a fuzzy intermediate stage.

    Fortunately, the long sea track ensures that any ex-hurricanes reaching the UK have gone through full transition before they arrive. The different amounts of available energy mean that even the most powerful of extratropical storms would barely make it onto the bottom of the hurricane scale.

    So that's how it works

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