AccuWeather.com Hurricane Center meteorologists, led by Meteorologist and Hurricane Forecaster Paul Pastelok, are predicting an active season for 2011 with more impact on the U.S. coastline than last year.
The team is forecasting a total of 15 named tropical storms, eight of which will attain hurricane status and three of which will attain major hurricane status (Category 3 or higher).
In a normal year, there are 10 tropical storms, six of which become hurricanes and two of which become major hurricanes, or attain winds that exceed 110 mph.
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2010's historic season had a total of 19 named storms and ranks as the third most active season on record, but there was little impact on the United States coastline. Twelve of these storms became hurricanes, five of which were major hurricanes. Two names from the 2010 season were retired on March 16.
"It looks like we're going to have more impact on the mainland of the U.S. coming up this year compared to last year," Pastelok said. "We had a lot of storms last year, but not a lot of impact [on the U.S.]."
In order to project the number of storms and impacts, the team looks at past years that have similar weather variables and patterns that closely resemble the most recent fall, winter and early spring months.
Factors for this Season
There are a number of physical drivers that have the team concerned for this upcoming hurricane season. These include:
--The orientation and position of the Azores and Bermuda high-pressure areas in the Atlantic
The Azores high is one of the bigger influences on the movement of tropical cyclones. High pressure systems alter the direction of a storm by steering the storm, a low pressure system, around it. This is one way forecasters can predict the track of a hurricane.
"The forecast position and strength of the Azores or Bermuda high is always a challenging forecast," Pastelok said. "An unexpected change could greatly alter where both early season and mid season storms track."
AccuWeather.com Expert Tropical Forecaster Dan Kottlowski added, "We do see some changes in the overall pattern across the Atlantic."
Kottlowski continued, "The water temps are not nearly as warm as they were last year, and also the upper air pattern looks slightly different... than last year, so that could have an impact as to where that subtropical high, that big high pressure area that helps guide tropical storms, sets up."
"It may weaken or actually reposition itself a little bit to the northeast as we get later in the season, which would allow more of a storm track closer to Florida and also up the East Coast," Kottlowski concluded.
--The future state of the ongoing La Niña
La Niña is a phenomenon that occurs when the surface waters in the central and eastern equatorial Pacific are colder than normal. La Niña results in low wind shear, especially in the main tropical development area in the Atlantic. Shear refers to strong winds that are high in the atmosphere. Wind shear is a "hurricane killer," in that it can hinder storm development as well as break up existing storms.
"Currently, right now we still are in a La Niña scenario, but it is starting to weaken," Pastelok said. "The signal is starting to show some signs of going neutral. That could have an impact on the westerly wind component down in the tropical Atlantic as well as the Caribbean. Stronger westerlies would prohibit major storms or a lot of storms, so it is a critical factor."
--The frequency and amount of dust that accompanies disturbances moving off the African coast
The presence of dust indicates dry air, which can hinder tropical development in the eastern Atlantic.
"Current projections on the weather pattern over Africa for this coming tropical season suggests there will be episodes of dust affecting development, but no more than normal," Pastelok said.
--A phenomenon known as Atlantic Multidecadal Oscillation (AMO)
AMO refers to the sea surface temperature in the northern Atlantic, and the temperature fluctuates from colder than average to warmer than average every few decades. Currently, the sea surface temperature is in the warm phase, and warm water is "hurricane fuel," in that it supports the development of tropical systems.
"We continue to observe the positive phase of the Atlantic Multidecadal Oscillation," said Paul Pastelok. "This will help to maintain warmer-than-normal water temperatures across most of the Atlantic Basin."
This Season's Concern Areas
As with most Atlantic hurricane seasons, the areas where storms are most likely to make landfall shift as the season progresses.
This year, the early season threat area will be the western Gulf of Mexico and the southern portion of the Caribbean. Within this zone, the higher concern for landfalls will be along the Texas and Louisiana coastlines.
As for the mid-to-late season zones, the eastern Gulf and Caribbean will be the focus. The higher concern areas will be the Florida Peninsula to the Carolinas.
"What we see is there is a clustering of storm impacts over the southeastern US, and that's the reason why we earmarked this as a concern area," said Kottlowski.
Another mid-to-late season concern for landfalls will be northern New England and the Canadian Maritimes.
"We feel that this season, there will be a higher potential for impacts across the southern part of the Basin into the Gulf of Mexico during the first part of the season," Pastelok stated. "This higher potential for impacts shift farther north into the southeast U.S. during the latter half of the season."
Hurricane season officially begins June 1 and ends Nov. 30.
For all the latest tropical information, be sure to check the AccuWeather.com Hurricane Center for the most up-to-date videos, information and storm tracks.
From AccuWeather.com (find the original story here); reprinted with permission.
