By Alex Sosnowski, Expert Meteorologist for AccuWeather.com
AccuWeather reports Subtropical Storm Ana has formed off the southern Atlantic coast of the United States, making it the first named tropical system of the 2015 Atlantic Hurricane Season.
A subtropical or hybrid storm has some warm, tropical features and some cool, non-tropical features.
Hurricane hunter aircraft began flights into the storm on Thursday morning. Ana, which formed late Thursday night, will affect part of the southeastern United States with rain, wind and rough surf through the Mother’s Day weekend as it reaches the Carolina coast.
Ana could gain full tropical storm designation with slight increase in strength by this weekend.
On Thursday, rain arrived well ahead of the storm along the Carolina coast. The rain will continue on and off into early next week. Winds and surf will increase from Virginia Beach, Virginia, to Daytona Beach, Florida, through the weekend.
Winds guiding the storm along are very weak. The center of Ana will wander close to the coast of the Carolinas with landfall likely later this weekend.
“The mostly likely area for the storm to wander onshore is between northern South Carolina and the southern tip of North Carolina on Sunday,” AccuWeather.com Hurricane Expert Dan Kottlowski said.
Since winds and rain extend well ahead of the storm, exactly where the center of circulation tracks will have little bearing on impacts.
Slow movement of the system will mean long-duration impacts. Rounds of drenching rain, gusty winds and rough seas will pester part of the coast, with the most significant conditions focusing on the Carolinas.
The risk to lives and property will be low for land areas, due to Ana forecast to remain a subtropical or tropical storm. However, there are some risks for people remaining on land and significant danger for those venturing in the surf or heading to sea.
“The slow movement of the storm will bring several straight days of periods of rain to portions of the Carolinas and perhaps southeastern Georgia, with the heaviest rain falling during the afternoon and evening hours,” Kottlowski said.
Rainfall averaging 2-4 inches in the coastal Carolinas will raise the risk of flooding on roadways and low-lying areas. Persistent onshore winds will also bring the potential for coastal flooding in portions of North Carolina and southeastern Virginia, particularly at times of high tide.
The constant bombardment of rough surf will lead to beach erosion focusing on North Carolina. The rough surf will cause frequent and strong rip currents, which will pose dangers to bathers.
While winds are not likely to become strong enough to cause widespread damage, there could be downed tree limbs, especially where locally gusty thunderstorms occur. A couple of brief tornadoes and waterspouts could be spawned by the storm. If and where these occur, damage could be more severe.
Since some strengthening of Ana is possible this weekend, prior to making landfall, winds will increase into Saturday along the Carolina coast. Winds will reach average an speed of 30-40 mph with gusts frequenting 50 mph and occasionally reaching 60 mph along the Carolina coast for a time this weekend. Gusts can be significantly higher in thunderstorms.
“Seas were averaging 8-12 feet offshore during early Friday and will translate to the coast in the form of very rough and dangerous surf into the weekend, before subsiding early next week,” Kottlowski said.
Seas will increase as the storm strengthens a bit.
Rough seas and squalls associated with the storm will make for dangerous conditions for small craft outside of protected coastal waters. Cruise ships will want to avoid the area of rough seas, which will extend from off the mouth of the Chesapeake Bay to near the northern part of the Bahamas and eastern Florida.
“While people should stay out of the water along the Carolina and Georgia coasts in this situation, this will be a storm for people to think of what they need to do for hurricane preparation for the upcoming season,” Kottlowski said.
Ana will help to strengthen an area of high pressure that will pump building warmth and sunshine in much of the East.
Direct impact from Ana as a subtropical storm is not likely to occur in the Northeast or penetrate hundreds of miles inland in the South this weekend.
Ana, in diminished form, could be pulled northeastward ahead of an approaching cool front across part of the mid-Atlantic and southeastern New England Monday into Tuesday. Ana’s moisture will become embedded with moisture from the front in the form of showers and thunderstorms.
The atmospheric roadblock will keep rounds of severe weather focused on the Plains this week, and the threat could ramp up even more over the weekend.
AccuWeather.com Chief Long-Range Meteorologist Paul Pastelok is monitoring the Atlantic Basin for additional development later in May.
“It is possible a tropical system slowly takes shape in the Gulf of Mexico during the third week of May along the tail end of a front with high pressure to the north,” Pastelok said.
AccuWeather has released its summer forecast for the U.S. and will release its Atlantic Hurricane Season Forecast for 2015 on May 13.
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