Flood risk from Andrea into evening; tornado watch S Md., eastern shore

* Flash flood watch until 10 p.m. | Rainfall totals from NWS *
* Tornado watch for southern Maryland through 8 p.m.*


Radar & lightning:Latest regional radar shows movement of precipitation and lightning strikes over past two hours. Refresh page to update. Click here or on image to enlarge. Or see radar bigger on our Weather Wall.

Overview: Through early afternoon, the rain has been soaking, but not swamping – the best kind. Amounts have generally about around 1.5-2 inches, plus or minus half an inch.

But as the core of tropical storm Andrea draws closer late this afternoon and evening, some flooding rains are possible, especially along and east of I-95. Rainfall totals (including what has fallen already) of 1-4″ west of I-95 are expected, and 3-6″ along and east of I-95.

Farther to the southeast, in southern Maryland, the southern Delmarva, northern neck of Virginia and points south, a tornado watch has been issued and is in effect through 8 p.m.

4:45 p.m. update: Rain continues, with the heaviest activity in southern Maryland (Calvert and St. Mary’s county). I’m concluding this series of updates.  See our PM Update for the latest outlook through this evening and the weekend.

4:00 p.m. update: About that tornado threat to our south – so far, not much happening.  Cloud cover has limited instability, squashing tornado potential. The National Weather Service’s Storm Prediction Center writes: IT/S NOT ENTIRELY CLEAR HOW MANY SUPERCELL STRUCTURES WILL ULTIMATELY EVOLVE ACROSS THIS REGION…BUT ISOLATED TORNADOES REMAIN POSSIBLE IF THEY DO…ESPECIALLY WITH ACTIVITY NEAR THE BOUNDARY OVER SERN VA.

3:27 p.m. update: Areal flood warning for southwest Anne Arundel and eastern Prince George’s county: stream gauge at Western Branch in Upper Marlboro at 8.3 feet and steadily rising.  Flooding possible in Upper Marlboro area this evening.

3:24 p.m. update: It’s becoming increasingly likely that it’s the areas east of I-95 that have to worry most about a particularly messy PM commute and possible flooding into the evening.  Both radar trends and model simulations show the axis of the heaviest rain moving up through the northern neck of Virginia into southern Maryland and then into DC’s eastern suburbs and finally up to around Baltimore.

gfs-radar

Note: the blue colors in the GFS model simulation indicate 0.75-1.75 inches of rain in that period. The yellow shade is 1.75-2 inches. (Model simulation from StormVistaWxModels.com)

I would not be surprised to see some flash flood warnings popping up soon for St. Mary’s, Charles and Calvert counties.

3:20 p.m. update: Incredible – Raleigh International Airport received 2.91 inches of rain in roughly an hour and a half (between 1 and 2:30 p.m.) according to the National Weather Service.

2:55 p.m. update: For those keeping track, the center of Andrea was about 70 miles northwest of Wilmington, N.C. at 2 p.m. Given its 28 mph rate of motion to the northeast, it’s probably about 100 miles north of there now.  Maximum sustained winds – mainly near and east of the center – are 45 mph. The National Hurricane Center says Andrea is “losing tropical characteristics.”  Here’s a satellite view:

andrea-fri

2:23 p.m. update: The area of rain for us to really watch for later is coming up from central North Carolina. Raleigh, N.C. received 1.18 inches of rain between 1 and 2 p.m. alone and a flash flood warning is in effect there (Link: Raleigh radar).  It might take until early to-mid evening for that rain to get here.

2:09 p.m. update: The City of Alexandria highlights the following areas as most vulnerable to flash flooding should heavy rains materialize later: “The greatest concern is the potential for flash flooding in vulnerable areas along Backlick Run (near the intersection of S. Van Dorn St. and S. Pickett St.) and Cameron Run (near and including Alexandria Tech Center and adjacent Eisenhower Ave.)”

2:00 p.m. update: A map of estimated rainfall from Doppler radar shows the heaviest totals, so far, have occurred right smack in the D.C. I-95 corridor with 2 to 3 inches from around Dale City through the District and into Laurel.

upper-2

1:40 p.m. update: Look at the sprawling area of the eastern seaboard covered in the rain from Andrea below.

swath

The area on radar for D.C. to watch, especially along and east of I-95, is due south.  As it moves north/northeast at about 30 mph, it may bring some flooding rain into the region late this afternoon and especially into the evening hours.

1:36 p.m. update: Here’s a map of the area under the tornado watch for locations to our south and southeast.

tornado-watch-s-md

Tornadoes are common in landfalling tropical systems, especially along and east of the track.  Yesterday, several tornadoes touched down in Florida.  Although  tornadoes from tropical systems are not typically as strong as those spun up by mid-latitude storms in the Plains, for example, they can be damaging.

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