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Posted at 02:35 PM ET, 08/30/2012

Will Hurricane Isaac’s remnants rain on D.C. over Labor Day weekend?

Model simulations of rainfall through Monday night (top) and NOAA’s estimate (bottom). Most have the D.C. area on the edge of substantial rainfall. (
As Isaac slowly scoots away from Louisiana Friday and into the southern and central Plains this weekend, we wonder: what comes next? Will some of its moisture eventually stream towards the D.C. area?

I think the answer is a qualified yes by late Sunday into Monday, but I’m not anticipating a major impact .

Isaac’s long journey through drought-plagued Arkansas and Missouri will squeeze out a good portion of its abundant tropical moisture before any of its effects can be felt in Washington.

Track forecast for tropical storm Isaac and its remnants (National Hurricane Center)
The National Hurricane Center’s official track forecast doesn’t move its remnant center into the Ohio Valley until Tuesday! And by then, it probably won’t have much of a center left.

Of course, Isaac has a large moisture field - so the decay of its center matters little in evaluating how and when pieces of it might feed into D.C..

It seems that the critical feature in determining Isaac’s effect on our area is a weak “back door” cold front sliding south from the Northeast. This front - initially moisture-deprived - is likely to stall over the mid-Atlantic beginning Saturday.

Weather map Monday morning showing Isaac’s remnants and a backdoor front over the mid-Atlantic. Black polygon indicates area most likely to receive some rain (National Weather Service)
As Isaac edges closer to the Ohio Valley - probably late Sunday into Monday - some of the remnant moisture from Isaac’s circulation might “hook-up” with the front.

As such we have a chance of intermittent showers and storms starting Sunday afternoon and continuing into Monday. Locally heavy downpours are possible.

I don’t expect a widespread deluge or a prolonged period of rain. And if the front sets up far enough south, it might rain hardly at all or any rain we get would result from Atlantic moisture not Isaac’s remnants.

This forecast is one which requires fine-tuning, so please check back for daily updates.

By  |  02:35 PM ET, 08/30/2012

Categories:  Latest, Tropical Weather

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