Near normal hurricane season predicted

The United States National Oceanic and Atmospheric Administration said Thursday that conditions in the atmosphere and ocean favour a near-normal hurricane season this year in the Atlantic Basin. 

NOAA no longer predicts exact numbers of named storms, hurricanes and major hurricanes in its annual late May forecast. Instead it gives a forecast on the six-month hurricane season – which lasts from 1 June until 30 November – based on probability.  

The forecast said there is a 70 per cent chance of nine to 15 named storms, four to eight hurricanes and one to three will become major hurricanes. Based on the period between 1981-2010, an average hurricane season typically produces 12 named storms with six hurricanes, including three major hurricanes. 

“NOAA’s outlook predicts a less active season compared to recent years,” said NOAA Administrator Jane Lubchenco. “But regardless of the outlook, it’s vital for anyone living or vacationing in hurricane-prone locations to be prepared. We have a stark reminder this year with the 20th anniversary of Hurricane Andrew.” Andrew, the Category 5 hurricane that devastated South Florida on 24 August, 1992, was the first storm in a late-starting season that produced only six named storms.” 

Although the Atlantic Basin is experiencing a multi-decadal cycle of increased hurricane activity that began in 1995, NOAA said that two factors now in place could limit tropical storm development this year if they persist. Those factors include strong wind shear, which inhibits tropical cyclone development in the area of that Atlantic Basin where most storms develop, and cooler than usual sea surface temperatures in the far eastern Atlantic.  

Another potentially inhibiting factor would be the onset of an El Niño in the Pacific Ocean. El Niño, which is a cyclical phenomenon that involved an anomalous warming of the sea surface temperatures in the equatorial central and eastern Pacific Ocean, is known to create higher wind shear in the Atlantic Basin and particularly in the Caribbean, hindering tropical cyclone formation and strengthening. Currently, some of the forecast models are predicting an El Niño to develop by the third quarter of 2012, the peak period of the Atlantic Basin hurricane season. Other models, however, predict what is called ENSO neutral conditions, which doesn’t normally impact the Atlantic Basin hurricane season one way or another. 

Tropical Storm Risk  

Another noted hurricane season forecaster, the UK-based Tropical Storm Risk, also issued its preseason outlook for the 2012 Atlantic hurricane season. 

“The outlook anticipates Atlantic basin and US land-falling hurricane activity being close to their long-term (1950-2010) norm values, but 10 to 40 per cent below their norm values for the last 10 years (2002-2011),” the forecast report stated. 

Tropical Storm Risk said there was a 34 per cent probability of an above-normal Atlantic hurricane season; a 36 per cent probability of a near-normal season; and a 30 per cent chance of a below-normal season. 

Quantifying its outlook, Tropical Storm Risk forecast 13 named tropical storms, including six hurricanes and three intense hurricanes.  

Tropical Storm Risk believes the United States is overdue for hurricane land-fallings and said it has a 48 per cent probability of above-normal land-falling activity.  

“At present the main climate indicators point to the 2012 hurricane season being close to norm,” said Professor Mark Saunders at Tropical Storm Risk. “However, uncertainties remain and we are overdue [for] US land-falling hurricane strikes. Only one hurricane (Irene) has struck the US in the last three years and no major hurricane has struck the US since Wilma in 2005. On average four or five land-falling hurricanes would strike the US in three years and four major hurricanes would strike over six years. Nature has a habit of correcting herself.” 

Early start  

Even though the Atlantic Basin hurricane season doesn’t officially start until 1 June, there has already been one tropical storm and there is the chance another tropical cyclone will develop before the end of May. 

The weather system that brought more than 14 inches of rain to Grand Cayman so far this week, and which has been designated Invest 94L by the National Hurricane Center, had lifted northeast toward the Florida Keys by Thursday morning and was given a 40 per cent of developing into a tropical cyclone. If it were to develop a closed circulation and sustained winds of 39 miles per hour or more, it would be classified as Tropical Storm Beryl. If this were to happen, it would be the first time in recorded history that there have been two named tropical cyclones before 1 June. 

The rain brought by the weather system to Grand Cayman starting Sunday has helped set an unofficial record for rainfall in May. The previous record for May was 16.14 inches in May 2002. Based on initial calculations, which are subject to verification at the end of the month, Grand Cayman had already received 16.69 inches of rain this month through Wednesday.  

Although cloudiness over Grand Cayman is generally expected to decrease on Friday, a 30 to 40 per cent chance of showers will remain through Monday. 

Changes at National Hurricane Center  

Bill Read, the director of NOAA’s National Hurricane Center, will retire on 2 June, the day after the hurricane season starts. His replacement will be Rick Knabb, who will start his duties on 4 June. 

Mr. Knabb, who worked for NOAA previously as the deputy director of the Central Pacific Hurricane Center in Honolulu and as a senior hurricane specialist at the National Hurricane Center in Miami, returns after serving as the on-air tropical weather expert for The Weather Channel since May 2010.  

The National Hurricane Center has also implemented a couple of changes for the 2012 hurricane season, including a slight modification of the Saffir-Simpson Hurricane Wind Scale.  

These changes don’t impact the classifications of tropical depressions, tropical storms or Category 1 or 2 hurricanes. However, Category 3 hurricanes will now range from having sustained winds of 111 to 129 miles per hour (the upper limit down 1 mph); Category 4 hurricanes will range from 130 to 156 miles per hour – from 131 to 155 mph; and Category 5 hurricanes will be classified as those with sustained winds of 157 miles per hour or more, up 1 mph. 

These changes were implemented to resolve number rounding issues associated with converting knots to miles per hour. 

In addition, the tropical cyclone forecast cone will be slightly smaller this year, indicating increased forecast skill of hurricane tracking.  

The size of the forecast cone has been reduced to reflect two-thirds of the historical forecast error over the previous five years. The circle radius in the Atlantic Basin ranges from 36 nautical miles at 12 hours out and 56 nautical miles at 24 hours out, to 236 nautical miles at 120 hours – or five days – out.