September 29, 2010: The nation's weather

A newly formed tropical depression in the northwestern Caribbean Sea, located south-southwest of Miami was expected to become Tropical Storm Nicole Wednesday as it progressed toward southeastern Florida.

It was forecast to move through the Florida Keys around midday and through southeastern Florida on Wednesday afternoon and night.

Moderate to heavy rainfall with strong wind gusts would continue to affect the Cayman Islands, Cuba, southern Florida and the Bahamas. Total rainfall accumulations were forecast 5 to 10 inches over the Cayman Islands, Jamaica and Cuba. Isolated maximum amounts of 20 inches were possible over the higher elevations of Cuba and Jamaica. Moreover, rain accumulations of 4 to 8 inches were possible over portions of extreme southern Florida and the Florida Keys. These rains could cause life-threatening floods and mud slides, forecasters said.

Moving northward, the cold front that pounded through the Eastern U.S. Tuesday was expected to become stationary along the East Coast on Wednesday as a blocking ridge anchored over the Western Atlantic. This frontal system combined with tropical moisture from the tropical depression or possible tropical storm would result in a significant rain event from Florida northward into the Mid-Atlantic on Wednesday, and then to the Northeast on Thursday. Very heavy rain was possible starting Wednesday afternoon over the Carolinas, spreading inland through the Mid-Atlantic states early Thursday.

In the midsection of the nation, a cold front was expected to drop southeast across the Central U.S. on Wednesday and Thursday. Showers and thunderstorms would be confined along the northern portion of the front across the Northern Plains, Upper Midwest and western Great Lakes.

Out West, a relief of the recent heat wave and all time record high temperatures was on its way as the ridge weakened and slowly moved eastward. Coastal regions would take a tumble and drop by 20 to 30 degrees as low clouds and fog returned and onshore flow developed. Inland areas would see a gradual cooling each day through Friday.

Temperatures in the Lower 48 states Tuesday ranged from a low of 20 degrees at Charleston, Nev., to a high of 110 degrees at Hemet, Calif.