Weekend Heat Before Isaac Rain in NYC, DC, Philly

By , AccuWeather.com Senior Meteorologist
September 1, 2012; 11:13 AM ET
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Heat and humidity will build over the mid-Atlantic this weekend ahead of any influence from Isaac as a tropical rainstorm.

High pressure responsible for the agonizingly slow movement of Isaac in the South will work to build heat from the Midwest to the Atlantic coast during the first part of the Labor Day weekend.

Temperatures will surge into the 90s in Washington, D.C., Baltimore, Philadelphia, New York City, Hartford and Boston on Friday.

While cooler air from Canada will burst the bubble of heat rather quickly across New England for the weekend, 90-degree readings will hold on from Philadelphia through Richmond, Va., during Saturday.

For some, it may feel more like the Fourth of July for a couple of days.

Meanwhile, the center of circulation of Isaac will continue to unwind into the weekend over the Midwest. However, it probably will not completely fade away.

AccuWeather.com meteorologists feel that at least some showers and thunderstorms associated in part with the system will drift in from the Midwest.

It will not be a simple matter of tracking the "blob" of moisture with Isaac as the rainfall will become embedded with a frontal zone sagging across the region.

The front and cooler high pressure pushing into New England will try to slow the forward progress of the rain once again, perhaps causing it to stall over the Ohio Valley and central Appalachians.

However, all things considered, the probability of showers and thunderstorms will increase over the mid-Atlantic Sunday and Labor Day with temperatures trending downward. Much of the time in New England is likely to be rain-free as the second high pressure area moves in.

Timing and how much rain is delivered by the aging tropical system have yet to be determined for the region.

As with any feature of this sort approaching, there is the potential of isolated heavy rainfall and locally damaging thunderstorms.

Isaac has produced a general 8 to 16 inches of rain in southeastern Louisiana and southwestern Mississippi with locally higher amounts. A half a foot of rain is forecast to reach into drought-stricken areas of Arkansas and Missouri into the weekend.

Locally damaging wind gusts are forecast to reach as far as southern Missouri with the aging tropical system.

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