Friday, August 3, 2007

Hazy, Lazy Daze of August


Sunny, hot, widely scattered showers. Once again today, temperatures were in the low 90s shortly after lunch time in most of the Washington metro area. A slight increase in humidity has helped widely scattered thunderstorms to develop, mainly southwest of the Beltway and in the immediate Baltimore metro area. At 4pm, Dulles and Manassas were reporting thunder and temperatures down into the 80s.

Hot temperatures and seasonable humidity are likely to continue through next week after a partial respite on Sunday.

Tonight and Tomorrow

Hot, humid, scattered thunderstorms. The chance of scattered thunderstorms will continue through this evening with overnight lows from the mid 70s downtown to some upper 60s in the 'burbs. Tomorrow will be a couple of degrees warmer than today with highs 94-98° and a 20% chance of scattered thunderstorms.

For the outlook through the rest of the weekend, scroll on down to Camden's post below.

Tropical Topics

The tropical wave over the western Caribbean and the low pressure area over the northeastern Gulf of Mexico are still disorganized, although gradual development is still possible for each of them.

Dr. William Gray's Colorado State Tropical Meteorology Project has issued a revised forecast for the remainder of the hurricane season; the Miami Herald has a review, "University team trims hurricane forecast". The new total season predictions vs. the May 31 forecast are (50-year average in parentheses):
  • Named storms: 15 vs. 17 (9.6)
  • Hurricanes: 8 vs. 9 (5.9)
  • Intense hurricanes: 4 vs. 5 (2.3)
  • Net tropical cyclone activity: 160 vs. 185 (100)
The probabilities of at least one major (Category 3+) hurricane landfall are (100-year average in parentheses):
  • Entire U.S. coastline: 68% (52%)
  • East Coast including Florida peninsula: 43% (31%)
  • Gulf Coast from Florida panhandle westward: 44% (30%)
The forecast has been lowered from earlier levels because of:
  • Cooler sea surface temperatures in the tropical Atlantic
  • Significant dust outbreaks from Africa
  • Expected cool neutral or weak La Niña conditions in the Pacific

No presentation by Dr. Gray would be complete without an attack on global warming, and the latest forecast is no exception. It contains about 2½ pages of arguments against the "many media references to recent papers claiming to show such a linkage" between global warming and hurricane activity. Despite the peer-reviewed publications by Kerry Emanuel and others to the contrary, Gray, whose techniques are purely statistical, nevertheless asserts, "We have no plausible physical reasons for believing that Atlantic hurricane frequency or intensity will change significantly if global ocean temperatures continue to rise."

Drought Deepens

The MarylandWeather blog reports that half the state is now in the "severe" drought category.

The global warming references are overstated, but the Montgomery Gazette this week reports on the effects of the drought on Potomac River kayaking. The MoCo Council is considering reinstating an emergency assistance program for the county's farmers.

Thursday, August 2, 2007

It's August. It's DC. Get Used To It.


Sunny, hot, moderately humid. Temperatures are in the low to mid 90s throughout the Washington metro area this afternoon, while dewpoints are near to slightly below the August average of 66°, so heat indices are mostly within a degree or two of the actual temperature. Leesburg was the local hot spot at 4pm with 97°, but the heat index was only 96°. Except for some very isolated showers in the mountains, radar is clear for several hundred miles.

Hot temperatures and seasonable humidity are likely to continue into the weekend.

Tonight and Tomorrow

Crank up the AC. Tonight will be mostly clear and quite warm with lows in the low 70s to near 75° in the city and some upper 60s in the 'burbs. Tomorrow will be sunny, hot, and seasonably humid with highs 93-96° and a very slight chance of late day thunderstorms.

For the outlook through the the weekend and beyond with Larson's Long-Range, scroll on down to Josh's post below.

Tropical Topics

The tropical wave which is now over the eastern Caribbean was looking more impressive on satellite images today, but was still disorganized. It still has some potential for development. A Hurricane Hunter plane was enroute early this afternoon to investigate.

Another area of interest is a batch of showers in the northern Gulf of Mexico.

The AP is reporting (via WaPo, for some odd reason under a "Global Warming" link) that "Ex-Hurricane Center Chief Wants Job Back". Ousted Director Proenza's lawyers are alleging in an 11-page letter that he was illegally fired.


The Weather Channel's Dr. Heidi Cullen was interviewed ("Into the Limelight, and the Politics of Global Warming") in Tuesday's New York Times about her career in climate research and reporting.

Photo courtesy New York Times.

Tuesday, July 31, 2007

Slight Respite from Humidity, But More Heat Ahead


Hot, a little less humid. The brightness of the sunshine and the sharpness of the shadows are signs that drier air has been gradually filtering into the region. Dewpoints in the immediate metro area were in the low 60s by mid afternoon, although the southern fringes of the region were still at or near 70°. Meanwhile, the extra sun has helped push temperatures to 90° or above at nearly all locations; Dulles and National were both 91° at 4pm. The nearest thunderstorms on radar are scattered between Charlottesville and Richmond and along the Virginia Eastern Shore.

The heat is likely to build through the rest of the week as more humidity returns as well.

Tonight and Tomorrow

Forecast Confidence: High-Very HighHot. Skies will be mainly clear tonight with lows in the low 70s to near 70° downtown and in the mid to upper 60s in the burbs. Tomorrow will be sunny and hot with highs 90-94°.

For the outlook through the rest of the week and into the weekend, scroll on down to Jason's post below.

Tropical Topics

Tropical Depression 3 developed overnight and quickly became Tropical Storm Chantal north of Bermuda this morning. The storm has strengthened to maximum winds of 50 mph as it scoots off to the northeast on its way to brushing by Newfoundland early tomorrow. It is likely to lose its tropical characteristics in the next 24 hours.

The tropical wave now about 520 miles east of the southern Windward Islands was less organized this morning, but it still has the potential to become tropically depressed in the next couple of days.

Cool Guys

This week's episode of the WaPo's Secret Worlds of Summer series profiles the "Faces Behind the Freeze".

Monday, July 30, 2007

More Heat, Less Humidity, Some Light


Warm, humid, widely scattered thunderstorms. Following yesterday's much-needed, if not exactly drought-busting rains (National 0.98", Dulles 0.54"), today's storm activity has been considerably lighter and mainly confined to east of I-95. National reported thunder for several hours and even some frequent lightning at mid afternoon, but no rain as of post time. A north to northeasterly wind indicates that the nearly stationary front is over the Eastern Shore and southeastern Virginia, but humidities are still quite muggy with dewpoints within a degree or two of 70°.

A few isolated storms are possible into the evening hours, then gradual clearing overnight. For the hotter and drier outlook through the rest of the week and into the weekend, scroll on down to Jason's post below.

Tropical Topics

The National Hurricane Center is keeping an eye on a tropical wave about 950 miles east of the southern Windward Islands. This area shows some signs of organization and has the potential to develop more in the next couple of days.

Some more light is being shed on the issue of a possible hurricane/global warming link described in Chris Mooney's just-published book, "Storm World". The discussion continues with the publication today of a peer-reviewed paper, "Heightened Tropical Cyclone Activity in the North Atlantic: Natural Variability or Climate Trend?" in the Philosophical Transactions of the Royal Society of London. This is a formal publication of data presented in a forum at the annual meeting of the American Meteorological Society in January. The analysis by Greg Holland of the National Center for Atmospheric Research and Peter Webster of Georgia Tech indicates that there has been a significant increase (see chart to the right) in Atlantic Basin tropical cyclone activity in the last century.

In press reports (see AP, via WaPo), however, an NHC "official" is quoted as saying that the research is "sloppy science". The reason this is controversial is (1) the sample size is so small, even over 100 years, and (2) there have been major improvements in observational technology over that time, most notably aircraft reconnaissance beginning in 1944 and satellite surveillance in 1970. Chris Landsea of the National Hurricane Center has some very interesting charts in a paper published in the May 1 issue of EOS, the Transactions of the American Geophysical Union. He shows, for example, that in the record-breaking season of 2005, storms were observed over nearly all of the Atlantic Ocean. In the previous record year of 1933, however, no storms were observed over the central Atlantic, where data was presumably much more limited.

Holland and Webster are not unaware of this possible effect and take it into account in their analysis. One point they make is that storms in the open ocean were less likely to be missed in the pre-satellite era because unsuspecting ships would accidentally encounter them. The most convincing argument, however, is that there are indeed several jumps in the storm frequency, but they occur at different points than the changes in technology.

This debate is likely to continue for a long time. Of all the possible connections to global warming, tropical cyclones are probably the most difficult to definitively analyze.

Chart by Steve Deyo, © UCAR

Seasonal Outlook

Latest seasonal forecast: Click here.

Latest 3-month temperature outlook from Climate Prediction Center/NWS/NOAA.