Sunday, May 20, 2012

Forecast for Monday, May 21, 2012

A coastal trough of low pressure will continue to retrograde westward tonight. This low is retrograding towards land due to a strong area of high pressure blocking it from escaping to the north and east, while actually pulling it into the Mid-Atlantic. Clouds will increase from southeast to northwest. This system is drifting very slowly and it may not be for awhile until showers reach the coastal areas of Southeastern New Jersey and Delaware. The showers and clouds should slowly spread into the interior throughout the day on Monday. Some lightning strikes have been observed offshore with this trough, and an isolated thunderstorm cannot be ruled out as some of the modeling suggests a bit of instability to feed on.  East winds will continue to gust in the 20 to 30 MPH range, especially in New Jersey and Delaware. This wind direction will also help to bring in moisture off of the Atlantic and when the actual system is not producing showers, some patchy drizzle is likely. Note that there will be a temperature contrast developing between the shore points and southwestern areas.

Meanwhile, a cold front is expected to slowly meander into the area Tuesday and remain into Wednesday. The blocking pattern in place to our east will also cause this front to slow down and prevent it from making much eastward progress once it sets up in the region, while interacting with what is left of the broad trough of low pressure that moved inland. This will likely mean numerous showers and thunderstorms during this period, especially after some minimal daytime heating occurs. Also, Tropical Storm Alberto (or what will likely become a post-tropical system) will begin to turn north-northeast at this point, probably passing out to sea. However, some of the moisture from this could get sucked up into the front and the broad trough in place, increasing further the moisture content in place. Therefore, any showers or thunderstorms could contain some heavy downpours. Without much steering motion, some thunderstorms could be slow movers and we may need to watch out for some localized flash flooding. On Thursday, the front will slowly sag south and east as the blocking pattern begins to break down. However, with the trough still not totally out of the area and front not terribly far away, a chance of showers and thunderstorms is in the forecast, most likely after a few breaks in the clouds causes some daytime heating.

Tropical Storm Alberto has become more exposed throughout the day, as it continues to move west-southwest. It does not appear as though this system will be able to survive for much longer. It will also be moving over cooler waters which will weaken it further. I expect the system to slow down some tonight, but not before getting within 75 miles of Georgia and within 100 miles of South Carolina. The system will begin to turn north-northwest on Monday as the blocking pattern shifts to the east of United States, allowing for other systems over land to not move much. Once the block shifts east, the system should be able to turn north-northeast, before dissipating as remaining moisture will become sucked up by nearby troughs. Interests along the coast of North Carolina should still monitor the progress of this system as the timing of the shift towards the north will be critical in determining how close this tropical cyclone gets to the coastal areas. It has the chance of not being totally post-tropical when it passes North Carolina’s coast.

High pressure is expected to dominate for Friday into Saturday. This will bring mostly sunny conditions, along with the opportunity for the region to warm up quite a bit. However, a cold front may arrive Saturday Night with a chance for showers and thunderstorms. There is a chance this is delayed into Sunday. The cold front may prevent a hot weekend from taking shape, although Saturday will be very warm.