Weather456's Tropical Weather Blog

2008 Atlantic Hurricane Season Outlook

By: Weather456, 4:16 PM GMT on March 22, 2008

2008 Atlantic Hurricane Season Outlook

Issued March 20, 2008 by W456

Main Indicators

ENSO
Rainfall Patterns over Western Africa
The North Atlantic Oscillation (NAO)
The Quasi-Biennial Oscillation (QBO)
Continuation of above average activity

Overview of Indicators

During El Nino, high SST over the eastern Pacific causes more deep convection there. The resultant outflow aloft enhances upper tropospheric westerlies over the Caribbean and western equatorial Atlantic. Consequently, the 200 mb anticyclonic flow necessary for tropical cyclones to develop is reduced. During Neutrals and weak to moderate La Nina, low SSTs over the eastern Pacific suppress deep convection there. The resultant subsidence enhances lift and weak to moderate upper level easterlies over the Tropical Atlantic Summer, which favors tropical cyclone development.

West Africa represents the birth place of most Atlantic tropical cyclones. It is also the origin of the West African Dust outbreaks known as the Sahara Air Layer. Wetter than normal conditions over Sub-Shara Africa indicate wetter and cooler tropical waves decreasing the temperature gradient between the sea surface temperature and the 700 mb wave axis and suppressing convection. However, wetter than normal conditions also indicate reduce dust phenomena during the season. Drier than normal conditions produces hotter waves at 700 mb and as they move over the cooler sea surface temperatures, the temperature difference is enough to initiate convection which is needed for cyclogenesis. Though, drier conditions over West Africa means enhanced African Dust.

The Positive NAO index phase shows a stronger than usual subtropical high pressure center and a deeper than normal Icelandic low. The negative NAO index phase shows a weak and further centralized subtropical high and a weak Icelandic low. Negative NAO values imply more ridging in the central Atlantic and a warm North Atlantic Ocean due to stronger southerly winds during this period. Positive NAO values imply more ridging in the Eastern Atlantic and cooler sea surface temperatures especiallu along the West African Coast. A stronger ridge also indicate the probability of drier conditions over West Africa.

During the QBO, Atlantic tropical cyclones are more frequent when 30 mb winds are westerly and increasing, rather than easterly and increasing. There have been 44% more hurricanes and 74% more hurricane days during the west as opposed to east phase of the QBO.

Overview of Current and Extended Conditions

The current ENSO forecast calls for a weakening La Nina from now till June. During the months of May to August, temperature anomalies are forecast to be slightly cooler to near neutral conditions. Weak to neutral La Nina favor a slight increase in both the number of hurricanes and their intensity. These neutral conditions will extend into the remainder of the season up to October, where warm anomalies mat take over.

Over the past six months, there have been drier than normal conditions over Sub-Shara Africa which will indicate hotter and drier African Waves and increase Saharan Dust. Hotter and drier waves are more favored to produce convection as they enter the Atlantic and I believe this maybe the case between dust outbreaks. Also, a more eastward and stronger subtropical ridge (Positive NAO) will favor drier and dustier conditions than a more westward and weaker ridge (Negative NAO). Currently, the NAO index is near neutral but forecast to enter negative values this April which may indicate cooler Central Atlantic SSTs but warmer SSTs west of 60W and east of 30W.

The current tropical winds between 30 mb and 50 mb over the Tropical Atlantic are easterly and that corresponds to a 50 yr average between 1950-1999 of 8.53 storms. Atlantic tropical cyclone activity is inhibited during easterly phases of the QBO due to enhanced lower stratospheric wind ventilation and increased upper-troposphere-lower stratosphere wind shear. However, the trend of these stratospheric winds is decreasing and if this trend continues, the July 50-30 mb winds will enter a more weak easterly to weak westerly phase.

The Forecast

Based on the above information, adjustments to the normal seasonal average can be made. The 1950-2005 NOAA average is 11.0 named storms, 6.2 hurricanes and 2.7 major hurricanes. An addition of 2 storms for weak La Nina to Neutral. An addition of 2 storms for hotter tropical waves and subtraction of 1 storm for enhanced Saharan Conditions. An addition of 1 storm for a negative NAO for April and a subtraction of 1 storm for current QBO conditions. An addition of 1 storm for continuation of above normal tropical cyclone activity of past hurricane seasons.

Preliminary Seasonal Forecast 15 named storms, 7 hurricanes and 3 major hurricanes.

Note: This forecast is subject to change and will be updated in April to inlcude SLP anomalies, 200 mb winds, 50 mb winds, sea surface temperatures and tracks.


Figure 1. CFS Seasonal Sea Surface Temperature Forecast


Figure 2. 6-month Accumulated Precipitation % of Normal

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Storm Lashes the West Coast of Europe

By: Weather456, 12:30 PM GMT on March 10, 2008

Storm Synopsis...

A 954 mb deep storm is currently pusing over the island of Ireland, producing gale-storm force conditions over the Atlantic between 45N and 54N...from 13W to the coast of Europe. Expect winds in excess of 50 knots and swells of 23-35 ft. Gale warnings with dangerous seas, all craft should excercise extreme caution over these seas. The storm is forecast to push into the Europe later today bringing heavy wind and light to moderate rain (1-2 in per hr) to the Southern United Kingdom and Northeastern France. After which, the storm will weaken and move into the North Sea, bringing moderate (20-30 knots) wind and light rain (less than 1 in per hr) to parts of Belgium, the Netherlands and Northern Germany and Denmark on Tuesday (there time) or 00Z-06Z Tuesday.

UK Storm System.....Image taken last night by NOAA-17 satellite



Storm battering the West Coast of Europe with high winds, heavy surf and rain.

Ocean scene live surf web cam
Lahinch, Ireland


Current Infrared Satellite Imagery



The GFS forecast showing a much weaker, but strong, storm over the Southern North Sea. Countries along the coast include Belgium, the Netherlands and the Northeast corner of Germany. Image valid 00Z 11 Mar 2008.




Ivansrvivr explains Atlantic Sea Surface Temperatures

456, I am fascinated by El Nino/La Nina and how it changes weather all over the world. Here's my take on the unusual SSTs in the atlantic and I will tie it in with La Nina and future tropical activity: the abnormally strong Bermuda high is responsible for all the atlantic anomalies. The cooler parts are upwelling from stronger than normal tradewinds in the central Atlantic. By the time those winds are nearing Florida they are making the clockwise northwest then northerly turn. The southerly flow is also being drawn off South America. While the stronger than average winds are having a cooling effect on the Carrib, those winds ase so warm they are counteracting whatever effect the upwelling would have over the Gulf Stream. (the water upwelled in the gulf stream warmer than the water at the surface anyway) combine the upwelling of warmer subsurface waters, and the very warm southerly wind that has been predominant here and you get an unusually warm Gulf Stream. Often when La Nina weakens, the eastern seaboard gets a bad hurricane season. The evidence is mounting for just such a scenario judging by the SSTs and the strength of the Bermuda High.



IMO, I agree with everything said above. Good job!

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Subtropical Development

By: Weather456, 12:52 PM GMT on March 06, 2008

Subtropical Development Possible?

A vertically stacked non tropical low pressure areas has been cut-off from the main westerly flow by a a strong bridging high pressure system over the Northeast Atlantic. As a result the system has become occluded. Recent visible imagery showed a band of convection wrapping around the northeast qudrant with a clear frontal band evident extending to the south. Also, low level cloud motion showed dry air advection occuring within the dry slot, which further supports a non tropical system. QuikSCAT observations indicated a define close circulation with associated gale force winds mainly to the northwest due to the interaction with the high pressure ridge. The system is forecast to move southward as the blocking ridge builds further to Western Europe. Furthermore, cyclone phase diagrams showed the system aquiring a shallow warm-core structure and a contraction of the radius of maximum winds.

Currently the system is embedded within a broad upper level trough that should halt movement in the next 12-48 hrs. If the system remains embdded within the upper trough, wind shear should remain low enough for development. Sea surface temperatures are currently 20C under the disturbance, so I expect development, if any, to occur as the system moves more southward into warmer waters. I have tempted to mentioned the AMSU-A passes which indicated a weak warm-core at 250 hpa, but I'm not 100% convinced by this.

Despite this, the enviroment does not appear favorable for tropical development and this is reflected in the cyclone phase diagrams, where the GFS fills the low pressure area in 78 hrs time.

This Morning's QuikSCAT pass


Goes-12 Visible Image taken 12:15 UTC or 07:15 EST with surface observations overlaid


AMSU-A Channel 7 Temperature (250 hpa) 24 hr ending 10:07 UTC 6/3/08


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Destination: The Caribbean

By: Weather456, 8:54 PM GMT on March 05, 2008

Cacun, Mexico

In the 1970s Mexico's ambitious tourism planners decided to outdo Acapulco with a brand new, world-class resort in the Yucatán Peninsula. The place they chose was a deserted sand spit offshore from the little fishing village of Puerto Juárez. Its name was Cancún.

In the last two decades Cancún has grown from a tiny jungle village into one of the world's best-known holiday resorts. The Mexican government sunk vast sums into landscaping and infrastructure, yielding straight, well-paved roads, drinkable tap water and great swaths of sandy beach.


Holiday Fantasyland: Cancún Hilton Beach and Golf Resort © Photographer: John Neubauer.

Jamaica
Ever since Errol Flynn cavorted here with his Hollywood pals in the 1930s and '40s, travellers have regarded Jamaica as one of the most alluring of the Caribbean islands. Its beaches, mountains and carnal red sunsets regularly appear in the sort of tourist brochures that promise paradise.

Unlike other nearby islands, it caters to everyone from beach bums to newlyweds: you can choose a private villa with your own secluded beach; laugh your vacation away at a party-hearty resort; or throw yourself into the thick of the island's life while experiencing the three Rs: reggae, reefers and rum.


View at sunset of Kingston, Jamaica's capital city © Photographer: Jerry Alexande

Aruba

This parched speck of an island off the coast of Venezuela has guaranteed sunshine and is blessed with beaches that make you say 'ahhh'. Tourism is the big business here and it's served in a double scoop of Latin coastal coasters and sun bunnies from North America and Holland.

Although large-scale tourism dominates the island (read: luxury resorts from here to sunset), there are still undeveloped areas on the exposed northern coast, and much of the interior is inhabited by nothing more than goats and contorted divi-divi trees.


Boat languishes in the tropical waters © Photographer: Bill Bachmann

Saint Kitts/Nevis

Two Caribbean island vacations for the price of one.

St Kitts is as hopping as Nevis is sleepy, but relaxation and a rum punch are requisites on both islands. The dual island nation may officially separate soon, but visitors can still enjoy a menu of plantation-cum-boutique hotels, palm tree-lined beaches and adventurous hikes.


A little dip in Friar's Bay Cove, south eastern St Kitts © Photographer: Jeff Greenberg.

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The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

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About Weather456

With a Bachelors Degree in Environmental Sciences (2009), began tracking tropical storms in 2002 and is now a private forecaster.