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Posted at 7:40 PM ET, 09/ 6/2008

Hanna is History

By Jason Samenow

*Coastal Flood Advisory until 6:30 a.m. Sunday for tidal Potomac and Chesapeake Bay*

News article: Tropical Storm Hanna Drenches Washington Region

Besides some lingering flooding from rising streams in a few spots, Hanna has finished its business here. Skies have rapidly cleared and winds are subsiding. After dropping generally 2-7" over the metro region and locally higher amounts of up to 8 or 9", Hanna will be remembered for its heavy rain and flooding. The winds, while gusty, were never a major impact. Peak gusts reached the 35-50 mph range.

Rainfall totals from the airports: BWI 1.72", Reagan 3.9" and Dulles 6.53."

The National Weather Service has a preliminary summary of rainfall totals and peak wind gusts from throughout the area.

rainfall validation.gif
A comparison of the Capital Weather Gang forecast and what actually fell. Estimated rainfall image courtesy Wunderground

Referring to the above image, keep reading for my take on how well we predicted Hanna's wind and rain...

The above image shows the Capital Weather Gang generally captured the pattern of the rainfall distribution, but was too far east with the axis of the heaviest rain by about 30-40 miles. We predicted the heaviest rain would be along I-95 and points east whereas it was along I-95 and 30 miles west. Our rainfall totals were also a bit low, but mainly in underestimating the very heaviest rain. The areas of moderate and lighter rain we forecast fairly well.

Our wind forecast was pretty close to being on target, although we probably overestimated wind speeds by about 5-10 mph area wide.

So we slightly overestimated the wind and underestimated the rain. Overall, I think we made a pretty good forecast with respect to the timing, evolution, and impacts of this storm -- but let us know if you disagree.

We'll be back with regular programming tomorrow, including the latest on Ike. Feel free to post your storm totals and any thoughts you have about our coverage of Hanna.

By Jason Samenow  | September 6, 2008; 7:40 PM ET
Categories:  Floods, Recaps, Tropical Weather  
Save & Share:  Send E-mail   Facebook   Twitter   Digg   Yahoo Buzz   StumbleUpon   Technorati   Google Buzz   Previous: Rain to Exit Stage Right; Winds Hang On
Next: Forecast: Drying Out After Deluge


As late as last evening on the way home from work, national forecasters were saying that it was posible that the storm would hit the Carolinas and head out to sea. I think your forecast was very well done, although did anyone see 10+ inches coming in P. Wm? I'm also very interested in your thoughts on the effect of big storms on teleconnections.

Posted by: flynnie | September 6, 2008 7:52 PM | Report abuse

I think that you guys did a great job at forecasting the storm! These things can be hard to predict, but you guys did pretty well.

The only thing I was surprised with is that we got almost 9 inches of rain. The woods behind our house was a river for a while. The water was also bubbling up through the little gap between the sidewalk and the curb. It was a little strange, but it's happened before.

Those of us that got the 8, 9, 10 inches of rain will remember Hanna for a while, I think. At least I will, but then again, I'm a geek, so I remember everything weather related that happens here. Hehehe.

Posted by: weatherdudeVA | September 6, 2008 7:55 PM | Report abuse

Bravo, per usual! My fiancee and I had the pleasure of driving all over Upper NW, Chevy Chase and Silver Spring from 8am to 3pm doing wedding-related tasks, and it was QUITE nasty. Glad that's over.

Now on to watching Ike and hoping his remnants stay far away from here...

Posted by: Rishi | September 6, 2008 8:02 PM | Report abuse

Flynnie: The Weather Service indicated isolated 10" totals were possible. While we didn't specifically forecast that, it doesn't surprise me. Tropical systems often produce very localized extreme rainfall totals.

I'm glad you caught the fact that we stuck with our story and did not waffle as the models were flipping flopping east and west.

Posted by: Jason, Capital Weather Gang | September 6, 2008 8:02 PM | Report abuse

Saw little to no wind here in Rockville, other than that, your forecast was dead on with rain and with the speed of how quickly this storm moved out of the area. Glad it's all over, and I'm looking forward to enjoying a beautiful day Tomorrow. Glad the weekend wasn't a washout.

Posted by: Havoc | September 6, 2008 9:29 PM | Report abuse

Jason, as usual you guys did a great job. Thanks to the CWG for the great information and details.

Posted by: David A. in Stafford | September 6, 2008 9:43 PM | Report abuse

Whew, glad that is over. Glad it wasn't worse either. Hope we get a bit of a chance to dry out before another one hits. Also, extremely glad I don't live in a basement apartment anymore. Finally, overjoyedly glad we have the Capital Weather Gang to turn to for all weather events -- big and small.

Posted by: ep | September 6, 2008 9:47 PM | Report abuse

Thank Capital Weather Gang for providing the most up to the minute good data I could find all day in Crisfield, Maryland.

Posted by: OfficerMancuso | September 6, 2008 10:02 PM | Report abuse

My inner editor insists that I leave an extra "s" here, so everyone knows I really meant to say "thanks".

Posted by: OfficerMancuso | September 6, 2008 10:04 PM | Report abuse

For here in western Fairfax County the heavy rain really started approx. 8:00AM, continuing to around 4:00PM, with at least half a dozen TORRENTIAL rainbursts lasting 5 or 10 minutes with very poor visibility. It's my guess that that's where most of our estimated 8 inches came from.
While winds were gusty at times all of the neighborhood yard & deck stuff stayed put without any special precautions.
The sun was trying to come out by 5:30PM. We witnessed considerable flooding in the local Cub Run park, with water over the bike path and the creek completely out of it's banks, carrying large tree trucks. The overflow areas were teeming with snakes, toads, frogs, tadpoles and turtles in a state of high agitation. Our local raccoons will dine well this evening.
We've enjoyed today's Weather Gang coverage. Thanks everyone for their "in the field" reports. We think we made the right choice just staying at home today!

Posted by: Centreville VA | September 6, 2008 10:08 PM | Report abuse

The "how well did we do?" post-game analysis is a much-appreciated feature of CWG. This is the best weather site anywhere!

Posted by: ~sg | September 6, 2008 10:12 PM | Report abuse

Fox 5 says Oakton had nearly 8 inches of rain, DCA 3.5.

My "under-forecast" was due to the fact that more rain fell in the normally weak western quadrants than would generally be expected in a tropical storm. Thunderstorms with this system were rare and occurred on the east side of the storm. This is generally true for a garden-variety tropical system at this latitude.

Posted by: El Bombo | September 6, 2008 11:29 PM | Report abuse

My rainfall total of 6.75 inches in Franconia, Virginia, exceeded that received from such well-known hurricanes as Fran (1996), Floyd (1999) and Isabel (2003). Thank goodness the deluge happened after an extended dry period and was spread out over many hours. Going into this season, regional hurricane history suggested that we would see bouts of tropical activity. By the end of this hurricane season, I may have to add additional storms to my book, Hurricanes and the Middle Atlantic States.

Posted by: Rick Schwartz | September 7, 2008 12:13 AM | Report abuse

The Huntington neighborhood in Alexandria (Fairfax Co.) got badly flooded, with more emergency evacuations and apparent damage.

I heard an unconfirmed report that Lake Barcroft released some water - anyone here know more about that?

Posted by: Huntington Mark | September 7, 2008 12:29 AM | Report abuse

Thanks for all the feedback. The user community is a big part of this blog's success...and speaking on behalf of the entire team, we appreciate your comments and participation before, during, and after the storm. Over 230 comments were logged.

Posted by: Jason, Capital Weather Gang | September 7, 2008 12:45 AM | Report abuse

The comments to this entry are closed.

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