Very active hurricane season still predicted

Despite a relatively calm first two
months of the 2010 Atlantic Basin Hurricane Season, forecasters are still
predicting a very active year in terms of tropical cyclone activity.

Colorado State University
scientists Phil Klotzbach and William Gray left their 2 June, 2010, forecast
unchanged when they issued their update on Wednesday. Tropical Storm Risk also
issued an update Wednesday, with levels of tropical cyclone activity almost
identical to its 4 June forecast, although somewhat lower than its 6 July
forecast.

Klotzbach and Gray are predicting
18 named storms, 10 hurricanes and five intense hurricanes with winds of at
least 111 miles per hour. Tropical Storm Risk predicts very similar numbers,
with 17.8 named storms, 9.7 hurricanes and 4.5 intense hurricanes.

During the first two months of
hurricane season, there were only three tropical cyclones, one of which became
Hurricane Alex and one that became Tropical Storm Bonnie.  Tropical Storm Colin formed Tuesday out of
Tropical Depression 4, but dissipated almost immediately.

Klotzbach and Gray maintained their
June forecast primarily because of unusually warm tropical Atlantic sea surface
temperatures and the development of La Niña in the Pacific Ocean. 

Rather than call the start of the
hurricane season calm, the two scientists said the tropical cyclone activity in
June and July was “approximately average”. 
In fact, they cited what activity there was as one of the predicting
factors for a busy season.

“Most years do not have named storm
formations in June and July in the tropical Atlantic, south of 23.5°N,” they
wrote in their update report. “However, if tropical formations do occur, it
indicates that a very active hurricane season is likely…. When storms form in
the deep tropics in the early part of the hurricane season, it indicates that
conditions are already very favourable for tropical cyclone development.”

Klotzbach and Gray also commented
on the formation of La Niña conditions, which are caused by anomalous cooling
of sea surface temperatures in the equatorial Pacific Ocean.

“We have witnessed the development
of La Niña conditions over the past couple of months and we believe that a
moderate La Niña will be present over the next several months,” the duo’s
report stated. “The trend toward La Niña conditions should lead to reduced
levels of vertical wind shear compared with what was witnessed in 2009.”

The persistence of anomalously warm
sea surface temperatures in both the tropical and North Atlantic, combined with
anomalously low sea level pressures, were other predicting factors in their forecast.

“Current [sea surface temperatures
anomalies] in the tropical Atlantic remains at near-record warm levels,” they
wrote. “These very warm waters are associated with dynamic and thermodynamic
factors that are very conducive for an active Atlantic hurricane season.”

The scientists stated that
anomalously low sea level pressures typically result in weaker trade winds that
are commonly associated with more active hurricane seasons.

The two predictors used by Tropical
Storm Risk were the forecasts for trade wind speed over the Caribbean and the
tropical North Atlantic during the period of July to September and the forecast
of sea surface temperatures in the tropical North Atlantic between August and
September.

“At present, Tropical Storm Risk
anticipates both predictors having a moderate to strong enhancing effect on
activity,” its forecast summary stated.

Tropical Storm Risk said there was
a 96 per cent probability of above average tropical cyclone activity during the
hurricane season, a four per cent chance of a near-normal season and no chance
of a below-normal hurricane season in terms of activity.

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