Tropical storm force winds, flooding threat heightened along I-270 corridor

I270 Forecast

Tuesday: Cloudy with rain continuing to become heavier throughout the morning into the early afternoon. The heaviest rainfall and strongest winds are expected to the east along I-95, where flooding and wind damage are most likely, improving as you head west. Conditions will be improving through the late afternoon into the early evening. Winds: Var. 10-20 mph, Gusts: 30-40 mph, High: 81 (77-83)

Tuesday night: Clearing skies and calmer conditions expected. Winds: L&V, Low: 64 (61-68)

Wednesday: Partly cloudy skies. Winds: NW 4-8 mph, High: 85 (81-88), Low: 65 (62-67)

Thursday: Partly cloudy with isolated showers and storms. Highs will be in the lower to middle 80’s with lows in the middle to upper 60’s.

Friday: Partly cloudy with scattered showers and storms. Highs will be in the 80’s with lows in the 60’s.

Saturday: Partly cloudy skies. Highs will be in the upper 80’s to lower 90’s with lows in the upper 60’s to lower 70’s.

Sunday: Mostly sunny skies. Highs will be in the upper 80’s to lower 90’s with lows in the upper 60’s to lower 70’s.

Monday: Partly cloudy with isolated showers and storms. Highs will be in the middle to upper 80’s with lows in the middle to upper 60’s.

Forecast Discussion

We’ve been gearing up for it since yesterday, and Isaias has finally arrived. The storm made landfall last night as a Category 1 hurricane, and the outer edges of its rainfall started falling across our region in the early morning hours. We currently have a Flash Flood Watch and Tropical Storm Warning in place for central and eastern portions of the viewing area, and here’s a breakdown of what we’re expecting. First, starting with rainfall, the rain out there now will steadily build through the morning, becoming heaviest in the 10 AM to 2 PM time frame. The worst of the rainfall is still expected to the east, along I-95, where 4-6” total could fall. From there, rainfall is expected to drop off sharply to the west. A line from Frederick County south into Fairfax County is likely to see 2-4” of rain, with only 1-3” expected along the western extent of the watch. Counties along and west of I-81 have been taken out of the watch as less than an inch of rain is expected.

In terms of wind, there hasn’t been much change here, as Montgomery and Fairfax Counties remain in a Tropical Storm Warning, along with the DC metro. Wind speeds late this morning into the early afternoon could reach 20-30 mph, gusting up to 35-45 mph. This is enough to cause some damage, so it’s something to watch for. Back to the west, winds could still get gusty, but we’re not expecting tropical storm force winds in any other locations. The potential tornado threat from this storm stays to our east thankfully. Another good thing is this storm will be a fast mover. As mentioned above, the worst conditions will be seen from 10 AM to 2 PM, but once that ends, the storm will basically be gone to the northeast, and we’ll have a much quitter end to the day and overnight.

Quickly looking at the rest of the week, we’ll have a dry day tomorrow with high pressure. A weak disturbance to the east will result in renewed chances of isolated to scattered storms Thursday into Friday while temperatures remain seasonal. Drier weather wins out over the weekend as temperatures rebound to near the 90 degree mark once again.

Stay safe and dry out there if you can today!

Meteorologist Damon Matson

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