Brace for rollercoaster ride this hurricane season

Professor William Gray (left) and Philip Klotzbach

BRIDGETOWN, Barbados, April 4, 2007 - Brace for an active Atlantic hurricane season, possible torrential rains, and flooding this year.

The warning from the United Nations specialised agency on meteorology which was based on a forecast of the El Nino Southern Oscillation (ENSO), an influential weather signal, came as private sector forecasters at the Colorado State University issued their prediction of nearly double the number of storms and hurricane of the normal long term average.

WMO FORECAST
According to the World Meteorological Organization (WMO) the most recent El Niño, the periodic weather pattern that can have repercussions around the world from torrential rains and floods in some parts of the world to droughts in others, has now ended and a transition to its mirror image, La Niña, is a substantial possibility, according to the latest United Nations forecast.

Both phenomena refer to large-scale changes in sea-surface temperature across the central and eastern tropical Pacific, with a warm pool located in the central and western Pacific expanding to cover the tropics during El Niño but shrinking to the west during La Niña. Thus La Niña (or cold episodes) produces the opposite climate variations from El Niño.

El Nino tends to suppress the formation of deep rain clouds in the Caribbean and hence suppress hurricane formation but La Nina achieves the opposition and is a major rain producing influence for the region.

“The observed rate of cooling has been more rapid than most models predicted,” the WMO said in its latest update. “Currently, several, but not all, models indicate the likelihood of an emerging La Niña over the next several months.”

WMO however cautioned that forecasts made at this time of year “notoriously lack skill” and the March-May period is often referred to as the “spring barrier” in the predictability of El Niño and La Niña, but there are indications that cooler than normal waters may prevail over the next several weeks in the central and eastern Equatorial Pacific such that a La Niña event becomes established. In such an event, given the timing in the year, the phenomenon would likely persist for much of the remainder of the year.

Experts have noted the presence of a substantial pool of cooler than normal water just beneath the surface of the central and eastern Equatorial Pacific and this is expected to reinforce, over the next few weeks, the already cooler than normal waters at the surface.

“The system at this time of the year is finely balanced and can be quite easily deflected from an apparent track, but the pre-requisite conditions appear to be in place for the development of a La Niña event,” WMO said. “The next 2-3 months will be crucial for determining whether neutral conditions continue, or a La Niña event does indeed transpire.”

El Niño conditions, which in December were forecast as likely to persist until at least March, dissipated rapidly during January and February. Prior to that climate patterns over several months displayed many characteristics usually associated with El Niño, including drier than normal conditions across many parts of Australia, Indonesia and Fiji, unusually heavy rains and flooding across parts of eastern Africa, and extended dry spells across many south-western parts of southern Africa.

KLOTZBACH AND GRAY
In their forecast, issued yesterday, the research tem comprising Philip Klotzbach, Professfor Bill Gray', and William Thorson has increased the number for Net Tropical Cyclone activity to 185 per cent of normal.

Translated into numbers they are expecting 17 named storms of which nine will become hurricanes and of the nine five will become major hurricanes with wind speeds in excess of 111 miles per hour. Klotzbach predicts that one of these major hurricanes is likely to make landfall in the Caribbean.

Over the 178 days of the official hurricane season, which runs June 1 to November 30, they expect 85 storm days, 40 hurricane days and 11 intense hurricane days.

In an average year there are 10 storms which span 49 days, six hurricanes which span 25 days, and 2 major hurricanes lasting five days.

They said that high sea surface temperature and a "rapid dissipation" of El Niño which has occurred over the past couple of months and present neutral ENSO conditions developing into a neutral or weak-to-moderate La Niña conditions during the upcoming hurricane season.