Forecast Factors for the 2012 Atlantic Hurricane Season

By Meghan Evans, Meteorologist

Apr 26, 2012; 12:55 PM ET

 

Picture of Hurricane Irene churning over the Bahamas on Aug. 25, 2011. Credit: NOAA/NASA.

Based on numbers of expected storms, hurricanes and major hurricanes and not factoring in potential impact to land, 2012 is expected to be less active than last year.
There are a couple of factors that have led the AccuWeather.com Long-Range Forecasting Team to forecast lower numbers of named storms this year.
Starting Out with Less-Favorable Conditions
Compared to 2011, this Atlantic Hurricane Season will start out with a less-conducive environment for tropical storms to develop. The official start of the season in the Atlantic is June 1.
Strong high-level winds are in place over the western and central Caribbean, promoting increased wind shear. If these high-level winds do not abate, increased wind shear will inhibit tropical storm development early in the season.
Strong wind shear, which is the change of wind speed or direction with altitude, causes building clouds to be tilted, restricting vertical development. Unless a tropical system has a vertically oriented core, its ability to develop are diminished.

The surface pressure across the Atlantic is not as low as it was in 2011, when there was below-normal surface pressure across the Caribbean. The surface pressure is now near to above-normal in the same region.
When surface pressure is lower, it promotes tropical storm development.
"If numbers are low early in the season, then overall numbers for the entire season will turn out lower than the forecast," AccuWeather.com Expert Senior Meteorologist Dan Kottlowski cautioned.
RELATED:
2012 Atlantic Hurricane Forecast: Near-Normal Storms, Close to Coast
Recap of 2011 Atlantic Hurricane Season
Transition into El Niño
A shift into an El Niño pattern is expected by the peak of the Atlantic Hurricane Season, which occurs around Sept. 11. El Niño is a phenomenon classified by above-normal water temperatures in the central and eastern equatorial Pacific Ocean. It is often associated with diminished development of tropical systems in the tropical Atlantic.
A favorable set-up for tropical development in the Atlantic features a large area of high pressure over the central Atlantic with strong westerly winds located farther north.
"A change to El Niño forces the westerlies to migrate farther south, causing increased [wind] shear that will diminish or perhaps shut down further development beyond September," Kottlowski said.

Forecast Factors for the 2012 Atlantic Hurricane Season

More Rain Slated to Dampen Northeast Thursday

By Bill Deger, Meteorologist

Apr 25, 2012; 6:20 AM ET

In the wake of a major early week storm that quenched river and reservoir needs for water in the Northeast, another system is slated to bring more rain to the region come Thursday.
Fortunately, a repeat of the damaging heavy, wet snow that fell over the Appalachians is not expected thanks to a surge of milder air.
The center of the storm will track from the northern Plains today to the Ohio Valley tonight, triggering some severe thunderstorms along the way.
Late tonight, the threat for gusty storms will wane as the storm transitions into more of a rainmaker from the Ohio Valley through the mid-Atlantic into Thursday.
Many areas from northern Kentucky and southern Ohio east through the Delmarva stand to have another 0.50 to 1.5 inches of rain, which will fall in frequent batches with some thunder rather than continuously like the region experienced on Sunday.
Depending on the track of the storm, the big cities along I-95 from Washington to Boston could be in for similar rainfall amounts as well.

A piece of atmospheric energy swinging into the storm as it begins to pull away will enhance the rain farther north over upstate New York and New England into Thursday night, with up to an inch possible here too.
Enough cold air filtering in behind the storm could change the rain over to snow for a time in the higher elevations from the Adirondacks to the mountains of Maine early on Friday.
The cooler air will not just be limited to New England to end the workweek. Temperatures that will have risen into the 60s by Thursday over the rest of the Northeast will be knocked back into the 50s on Friday, along with a gusty wind that will make it feel even colder.
The unsettled pattern looks to continue into the first half of the weekend, as another storm could deliver more showers to the mid-Atlantic for Saturday.

More Rain Slated to Dampen Northeast Thursday

AccuWeather.com - Brett Anderson | Updated Computer Model Forecast for the Summer

Apr 10, 2012; 9:31 PM ET

The updated ECMWF long range seasonal forecast was released yesterday. In addition to the temperature and rainfall anomaly forecast for the summer, the model also shows......

1. ENSO phase shifting to weak/moderate El Nino by the end of summer according to its ensemble forecast.

2. Below-normal tropical activity in the central Atlantic (less Cape Verde storms), but slightly above normal activity off the Southeast U.S. coast as storms may form not too far off the coast instead of long tracking ones that form over the central Atlantic.

3. Above-normal temperatures over eastern North America for the first half of Fall.

The views expressed are those of the author and not necessarily those of AccuWeather, Inc. or AccuWeather.com

AccuWeather.com - Brett Anderson | Updated Computer Model Forecast for the Summer