Summer Continues Going Out Like a Lamb

Now

Excellent. Temperatures in the Washington metro area were mainly in the low 80s at mid afternoon, although a few spots were only in the upper 70s. Dewpoints are quite pleasant, and the radar is dry for hundreds of miles in all directions.

Tonight and Tomorrow

More of same. Lows tonight under mostly clear skies will be near 65° downtown to some upper 50s in the cooler 'burbs. Tomorrow will be sunny with highs much like today's, in the low 80s.

Scroll down to Josh's post below for the outlook through the weekend and beyond with Larson's Long-Range.

Tropical Topics

Florence's expected strengthening has been delayed; maximum winds were still 50 mph through the 5pm advisory. The storm's large breadth, however, means that tropical storm force winds extend as much as 400 miles from the center. The forecast track continues to show it moving northward near, and to the west of, Bermuda. Recent forecasts have been bringing the track gradually closer to the island.

Climate Clues

A new study published in today's issue of the journal Nature offers more insight into the feedbacks associated with global warming, and the news is not good for advocates of complacency. The article, "Methane bubbling from Siberian thaw lakes as a positive feedback to climate warming", describes the results from a new, more accurate, method of measuring the release of methane from thawing permafrost. The data show that the rate of methane emission may be 5 times as large as previously estimated. This is especially significant for the greenhouse gas budget of the atmosphere because tremendous quantities (tens of billions of tons) of methane have been stored in permafrost for tens of thousands of years, and methane is 23 times as effective in trapping heat as CO₂. The original article requires a subscription, but Nature has published an online news article discussing the results. Other news articles are available from:

• The Beeb: "Methane bubbles climate trouble"
  
• National Geographic: "Methane Belches in Lakes Supercharge Global Warming, Study Says"
  
• New Scientist: "Siberia's pools burp out nasty surprise"

(Both the Paper of Watergate and All the News That Fits We Print seem to have been content to join the Benton Crier in reprinting the Associated Press story online.)

Fine Late Summer Weather

Now

Improving. This morning's gloomy haze and mist have yielded to mainly sunny skies and temperatures in the pleasant mid 70s with only marginally muggy dewpoints in the low 60s. Radar at mid afternoon showed some very isolated showers from near Charlottesville to the Annapolis vicinity.

Tonight and Tomorrow

Very fine. Lows tonight under partly cloudy skies will be in the low 60s downtown to the mid and upper 50s in the 'burbs. Tomorrow will be sunny and pleasant with seasonable highs in the low 80s.

Tropical Topics

Florence was looking more organized today, and the storm's strength increased to maximum winds of 50 mph this morning. It is still expected to become a hurricane, possibly by tomorrow, but the forecast track turns it northward near longitude 67W (southwest of Bermuda) this weekend.

Mediarology

Capitalweather.com's Andrew Freedman reports that The Weather Channel is starting a broadband climate channel called One°. You can display a preview with Dr. Heidi Cullen at their web site. The online channel is part of TWC's new "initiative to disseminate information on climate change and global warming", as described by Broadcasting & Cable's web site.

As part of this initiative, a new program called "The Climate Code" hosted by Dr. Cullen will begin broadcasting October 1. It will air at 5pm ET on Sundays.

In addition to weekly interviews with other scientists, policy makers, and opinion leaders, The Climate Code will feature segments highlighting different aspects of the world's climate. The features will examine what people can do to help the environment; debunk some of the popular myths around the climate; look at how scientific understanding has changed in recent decades; and explore technological advances that can benefit everyone.

Cullen's recent presentation to the National Association of Black Journalists in Indianapolis was reviewed by Boston Globe columnist Derrick Z. Jackson.

Photo of Heidi Cullen from climate.weather.com

Bad Hair Day

5:20 Update: Some bright sun is now breaking through here north of the Beltway in MoCo.

Now

Cloudy, damp. The heavy rains of this morning have been replaced this afternoon by a drizzle, heavy at times, which is hard to pick up on radar but is very noticeable on your glasses if you go out walking in it. National picked up a very respectable 1.73" of rain by 11am, and Dulles had 1.34". This means that in the last 5 days the total precipitation has already exceeded the average amount for September by over 0.6". Temperatures in the mid 60s and dewpoints to match have put the relative humidity near 100%, and fog has been very prominent in the Live Shot to the right. Here at Afternoon Blog Central in MoCo, however, the sky has been brightening quite a bit in the last hour or so.

Tonight and Tomorrow

Gradual dryout. Drizzle and possibly a shower or two should taper off overnight. Lows will be near where they are now in many places, mainly in the low 60s. Tomorrow will see gradually decreasing clouds and highs in the upper 70s.

Tropical Topics

TD 6 was named Florence as of 11am this morning. It was a minimal tropical storm with top winds of 40 mph; winds have increased to 45 mph as of the 5pm advisory. Florence is notable at this point for being rather large in area. This means that it will be slow to develop, but with favorable conditions, it could develop into a major hurricane, as some models are now suggesting. The expected track puts it well east of the Bahamas as a hurricane this weekend.

Photo of TD 6 around 7am this morning from NOAA GOES satellite, via NASA GSFC in Greenbelt.

"I Want My TWC"

If you couldn't find The Weather Channel at the usual channel 30 spot on Comcast Montgomery analog cable this morning, it's been moved to channel 98. The move is part of a large game of musical chairs to make room for MASN coverage of the Nats, along with the extra $2 a month being added to your bill as a result. Comcast's own CN8 news/entertainment channel is replacing News Channel 8. Among the other moves: banishing HBO from channel 38 to digital only. Comparable changes are also being made in the digital channel lineup and on other Comcast systems.

Hello, Ernesto ... the Rain and Wind Arrive

11:59pm Update: The Flash Flood Watch has expired. Another .25"-.75" as rain tapers overnight. Look for steadier showers to end by the 6-9am range, and winds dying down to 15mph (with some occasional gusts) for the bulk of the day tomorrow. Maybe a few breaks in the clouds during the late afternoon and high temps near 75. -Dan Stillman
5:30pm Update: A band of heavy showers just east of Upper Marlboro and Bowie is moving northward.
4:15pm Update: National reported a wind gust of 46 mph (40 kt) in the past hour. Total rainfall is just under 1". Rain has ended at Norfolk.

Earlier

A Flash Flood Watch continues in effect through late tonight for most of Maryland, DC, central and northern Virginia, and the eastern panhandle of West Virginia. A Wind Advisory is also in effect. Click on your county above for details. CapitalWeather continues to call for a storm total of 2-5" in the metro area, probably the lower end of that range for DC and points west, before tapering tonight.

Ernesto was downgraded this morning to a tropical depression, and the last National Hurricane Center advisory was issued at 11am. The heaviest rain so far in the Maryland, DC, Virginia region has been in the Tidewater area, where Norfolk has picked up nearly 9" since 2am this morning. Official amounts in the immediate Washington metro area were near 2/3" as of early afternoon. Light to moderate rain will continue this afternoon. As the storm moves northward, some heavy rain bands will rotate northwestward into the area, especially east of I-95. Some wind gusts with these could exceed 40 mph, possibly causing some tree damage and power outages.

Scroll down to Camden's earlier post for more details, the latest radar, a storm total forecast map, and the extended outlook through the holiday weekend. Let us know what's happening in your area using the comments link at the bottom of this post, and stay tuned to CapitalWeather.com's continuing coverage of this developing event.

DC Braces for Heavy Rain Event; Ernesto Strengthens Approaching Carolinas

Now

Cloudy, cool. As Tropical Storm Ernesto nears the Carolina coast, a Flash Flood Watch is in effect through late Friday night for most of Maryland, DC, central and northern Virginia, and the eastern panhandle of West Virginia. Click on your county above for details. A state of emergency has been declared for the state of Virginia to allow deployment of the National Guard and other resources. For the latest satellite/radar loop from WUSA-TV9, click here.
[Note that the hurricance "warning" in the WaPo article linked above is bogus as of post time; it is in fact a watch.]

Those clouds you're seeing this afternoon are from a frontal system that stretches through the Carolinas, but radar and satellite images show the beginnings of a merger between that system and the outer fringes of Ernesto to the south. Temperatures are generally between 70° and 75° throughout the metro region this afternoon. The relatively drier northeasterly wind over the Mid Atlantic area has kept precipitation today confined mainly to southern Virginia southward.

Tonight and Tomorrow

Ernesto's rain and wind arrives. Tonight will be cloudy and cool with an increasing breeze, lows in the low to mid 60s, and a 40% chance of a few scattered showers through midnight. By morning, the chance of showers increases to 70% and with more coverage. Rain will be steadier and heavier during the day tomorrow with a chance of some thunderstorms and winds in the 15-25mph range. Highs will be in the upper 60s to near 70. In his post below, Josh has more details on the possible timeline for Ernesto impacts on the metro area, as well as the forecast through the holiday weekend and next week.

Tropical Topics

Ernesto regained strength over the Atlantic overnight and was a strong tropical storm with maximum winds of 70 mph by early this afternoon. It remained at that strength at the 5pm advisory. The storm is headed for landfall tonight near the North Carolina/South Carolina border. As it moves northward, the track will be deflected to the west by a strong high pressure area now centered in eastern Canada. This will also slow down the forward progress of the storm and enhance the precipitation in some parts of the Mid Atlantic area. Paradoxically, it's the relative weakness of the storm which will help increase precipitation amounts by preventing it from barreling off to the north as stronger tropical systems frequently do when they reach middle latitudes.

There is still some disagreement between models on the placement of the heaviest precipitation. The global model from this morning has the precipitation bullseye near the mouth of the Chesapeake Bay, but this afternoon's North American model puts the heaviest amounts from central Virginia to eastern North Carolina with a very sharp cutoff to the northeast. This model has amounts generally less than an inch through Saturday night north and east of the Potomac.

Stay tuned to CapitalWeather.com's continuing coverage of this developing event.

Eagerly Eyeing Ernesto

Now

Cloudy, cool. A Flash Flood Watch is in effect from Thursday afternoon through late Friday night for most of Maryland west of the Bay, DC, central and northern Virginia, and the eastern panhandle of West Virginia. Click on your county above for details. (And don't forget to check your gutters, since they've had plenty of time to collect debris over the last several weeks.)

Under cloudy skies and a northeasterly breeze, this afternoon's official Washington temperatures have failed to reach the 82° observed at 1am last night. In the southern portion of the metro region, however, low 80s and even a few mid 80s have been seen at Fredericksburg, Stafford, Culpeper, Manassas, and Winchester.

Radar shows some light to moderate showers and some heavier thunderstorms from eastern West Virginia southeastward to north of Richmond on I-95 and toward the Northern Neck of Virginia. These are moving generally northeastward toward the metro area.

Tonight and Tomorrow

Cool, some showers likely. Tonight will be cloudy and cool with a 50% chance of showers, especially in the southern and western suburbs this evening, and lows in the low to mid 60s. Tomorrow will be cloudy with a 40% of showers and highs in the low 70s.

Scroll down to Dan's post below for the outlook through the holiday weekend, and look for Larson's Long-Range later.

Tropical Topics

Ernesto continued to weaken over southern Florida last night and was declared tropically depressed this morning; peak winds were only 35 mph at 2pm and again at 5pm. Some strengthening is possible as it re-emerges over the Atlantic, so tropical storm warnings have been extended along the northern Florida, Georgia, and Carolina coasts as far as Cape Lookout, NC.

The main threat from this storm is clearly heavy rain rather than wind, although winds will increase as it moves northward and a stronger pressure gradient develops with a "blocking" high pressure area to the north. Although the exact path of the center of such a weak circulation is not that significant, recent forecasts have tended to push the track westward over the mountains as it approaches our latitude. Models are notoriously unreliable in forecasting amounts of this kind of convective precipitation, but some areas are definitely going to be very wet. The most likely locations for the heaviest rain are from central North Carolina through central Virginia and westward to the eastern slopes of the Blue Ridge.

The Importance of Being Ernesto

Now

Muggy. A tornado watch is in effect to the northeast of the immediate DC area until 8pm. Nearby areas affected in Maryland include Baltimore City/County as well as Anne Arundel and Howard Counties.

Temperatures in the low to mid 90s and dewpoints as high as the mid 70s have pushed some heat index readings over 100 in the Washington metro area this afternoon. After holding at 91° with a southerly river breeze, the National Airport temperature popped up to 94° at 4pm with a more westerly wind direction.

Despite the juicy conditions and a weak low pressure area to the north, regional radar is not very impressive so far. A few very isolated showers had popped up by mid afternoon, mainly to the north and east of the Beltway. The heavier activity was just east of the Blue Ridge and south of I-66 in Virginia. This area has now moved eastward to I-95 south of the Beltway. Technically, the area's 2-week-plus rainless streak was broken by the 0.01" which fell around 6am this morning, but there are probably very few lawns which would be convinced of that.

Tonight and Tomorrow

Chance of thunderstorms, then cooler and less humid. There is a 40% chance of showers and thunderstorms through this evening. Lows will be in the lower 70s in the city, near 70° in the cooler 'burbs, with gradually decreasing humidity. Tomorrow will be cooler and less humid with highs in the low 80s.

The outlook for the rest of the week and weekend is strongly dependent on the interaction of a northward-moving Ernesto with a high pressure area building to the north. Dan will update the outlook in his post tomorrow.

Tropical Topics

Ernesto has maintained relatively minimal tropical storm strength (45 mph at 5pm) today moving northwestward across the Florida Straits, although it has been looking more respectable on radar and satellite imagery. At mid afternoon, radar showed outer rainbands from the storm reaching across the Florida Keys northward as far as Naples and Fort Lauderdale. There is a slight chance of strengthening before landfall in south Florida, but the storm has a better chance of getting back to hurricane strength after re-emerging over the Atlantic before making the next landfall in the Carolinas.

The storm's possible effects on the DC region have varied in the last 24 hours between missing most of the rain because the storm moves offshore from the Outer Banks to missing most of the rain because the remnants move west of the mountains. The latest track has now veered somewhat to the east again, closer to the local area. Stay tuned as the situation continues to develop.