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Killer Timing: Two Splendid Days for the Weekend
Powerful Hurricane Dean Headed Towards Yucatan

Guest Blogger @ 9:30 AM

by Ryan Sobash

To the untrained eye, yesterday's cold frontal passage may have gone unnoticed. A handful of showers brushed the south and east suburbs late in the afternoon, but most areas, as has been the norm recently, remained sunny and dry. The more noticeable changes will become apparent this weekend.


Nice Day StampLow humidity, sunny skies, gorgeous! Well behind Friday's cold front, northwesterly breezes will filter in a gem of an air mass today with dew points plummeting into the 40s by afternoon. High temperatures will be appreciably lower as well, ranging from 80-84 under cloud-free (fair weather cumulus aside) skies. The evening and overnight are shaping up to be second to none, as temperatures slip to near 60 in the district (June 23rd was the last occurrence of a low temperature below 62), with northern and western locales settling into the middle 50s by Sunday morning. Heading to see the Nationals (7:05 pm) or the Redskins (8:00 pm)? Expect temperatures to be 72-76 for kickoff/first pitch - only concern is the heavy demand expected on Metro and southeast roadways. Make sure your windows are wide open tonight before heading to bed.


Forecast Confidence: HighLet's do it again.Refreshing conditions will continue into Sunday after a, dare I say, cool start. Temperatures will climb into the upper 70s to near 80 by mid afternoon. Increasing clouds from a disturbance originating in the upper Midwest will provide a chance for a shower well after sunset, and will keep overnight temperatures in the middle 60s.

So Far, The Dean of Hurricanes

Hurricane Dean opened it's eye for the first time Friday evening and, in doing so, strengthened into a Category 4 hurricane. Dean was the season's first hurricane (becoming one Thursday morning) and it's apparent that it wants to be remembered for being the season's strongest. Dean's track between St. Lucia and Martinique as a Category 2 storm claimed three lives as winds tore off roofs and mudslides crushed homes and property. Thankfully for the Windward Islands, Dean is moving along at breakneck speed, cruising into the Caribbean at over 20 mph (a sprint as far as hurricanes go in the tropics), but is expected to slow in the coming days.

Pictured: A satellite image of Hurricane Dean shortly after the eye became visible. Image courtesy of NOAA.

Of course, all eyes are on the future track of Dean. The official National Hurricane Center (NHC) track takes Dean across the island of Jamaica as a Category 4 hurricane, although met with the same prediction, Hurricane Ivan chose to dance around the island in 2004 (nonetheless, damage was still significant). Given that the NHC issues an official forecast track, it is prudent to recognize that hurricane track forecasting, like all of meteorology, is far from a perfect science (hurricane intensity forecasting even less so). Taking this into account, the official forecast contains a cone of uncertainty that surrounds the track. Experts commonly advise the public not to focus on the line in the center. The uncertainty in the track forecast is normally gauged by assessing the spread in various computer model forecasts. Television meteorologists and other journalists are becoming increasingly adept at using graphics that include a sampling of the model forecast hurricane tracks. The popular internet news website has even featured a link to such a graphic throughout its coverage of Hurricane Dean (see graphic below).

This graphic shows fifteen projections of the forecast hurricane track. A few notes:
  • XTRP, the black dashed line, is simply an extrapolation of the Dean's forecast speed and heading (likely to change).
  • NHC is the official forecast track, which has been determined using the other forecast guidance.
  • It is clear that the models possess differences in both eventual path and speed. The models are in good agreement from Dean's initial position until it passes 80W (hence, why the cone gets larger).

A collection of forecast model hurricane tracks for Hurricane Dean from Friday evening. Image courtesy of the South Florida Water Management District.

The latest version of this graphic can be found here.

Ryan Sobash is currently employed as a meteorological developer in the Meteorological Development Laboratory at the National Weather Service in Silver Spring, MD. He gained his B.S. in Meteorology from Penn State University in May 2006 and is working towards a M.S. in Meteorology at the University of Oklahoma, projected to be completed in May 2009.

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