Thursday, 11:30 a.m.
The 2013 Atlantic Hurricane season is not yet a week old, yet we have the first named storm of the season in Andrea. The storm is quickly approaching the west coast of Florida and will move inland this evening. The broad upper-level trough over the Mississippi Valley continues to induce a southwesterly flow over the tropical storm, and while those winds have been weak enough over the past 24 hours to allow for some development of Andrea, they've also been strong enough to put a cap on how strong it can get. There's also a fair amount of dry air wrapping around the south side of the storm, so that, too, will help to keep a lid on how strong the storm can get.
While tropical storm-force winds will rake across the Florida Peninsula this afternoon and some tropical storm-force winds are likely in the vicinity of the track of the storm up through southeastern Georgia and the eastern Carolinas tonight into tomorrow, the main impact of the storm will be its rain. Here are the latest rainfall projections going forward through tomorrow night:
Flood or flash flood watches abound from Florida up through southern and eastern Georgia into the Carolinas. Some of these areas have already picked up several inches of rain, so the additional heavy rain fall will likely contribute to flooding.
There are two aspects of the storm, though, that will help to limit the flood potential. One of them is the forward speed of the storm. Now at a steady 15 mph, it will only increase that speed tonight and tomorrow as it gets farther and farther north and is caught up in the westerlies. That means the heaviest rains won't persist for an extended period of time.
In addition to the speed of the storm, the strength it now possesses means a more consolidated rain shield directly associated with the storm. That essentially means there will be somewhat less rain in the Appalachians, probably not enough to warrant flooding in to many areas from northern Georgia up into Pennsylvania.
Once beyond Andrea, the main story will be a drying out of the pattern and an expansion of the heat that is currently baking the West. Here's a look at the projected temperature anomalies for Friday across the country:
By the end of the weekend, the upper-level ridge will build back over the Rockies, and the cool air on the Plains will be erased. Here's the 12z 6 June NAM model 500mb forecast for Sunday evening:
With that upper-level low moving into southern California over the weekend, the heat will be quelled in much of the state, particularly over the southern reaches, while the heat steadily expands across the Rockies toward the western Plains. The Monday anomalies show that heat moving out into the Plains:
It will take quite a while for that heat to reach the East. At least the eastward migration of the upper-level ridge will mean a greatly reduced risk of severe weather on the Plains this weekend into next week.
Two systems will delay the onset of warm weather in the Ohio Valley and the East over the next week or so, but then it should get warm all across the country heading into the Memorial Day weekend.
A turn to much colder air over the Northeast and mid-Atlantic states will set the stage for a rain and snow storm later this weekend before it turns much warmer later next week.
It's warm now, but will turn much colder this weekend, with a storm threat later Saturday into Sunday. Warmth will return by the second half of next week.
Though it is cold now east of the Mississippi, with a couple of opportunities for snow into the weekend, a blast of warmth is due for much of the country east of the Rockies next week.
Warm air will once again surge eastward from the Plains to the East Coast this weekend and early next week. A strong storm next Tuesday and Wednesday will then be followed by colder air later next week.
A storm in Southeast Texas will generate severe thunderstorms this afternoon and tonight, and some wet snow on its western flank as it heads into the Ohio Valley tomorrow.