Statement as of 5:00 am EDT on August 17, 2007
The convective organization of Dean is not very impressive in either satellite imagery or imagery from the French radar on Martinique. There are only occasional glimpses of a ragged eye on radar...and the eyewall has been at best about 50 percent coverage. Satellite intensity estimates are 77 kt from both TAFB and SAB...which are unchanged from earlier. The initial intensity will remain 85 kt for this advisory...but it is possible this is a little generous. The initial motion is 275/21. Dean is on the south side of a deep-layer ridge...and this should continue for the next 72 hr with Dean remaining on a general westward to west-northwestward track. The large-scale models have seemingly responded to the G-IV jet mission by showing a slightly weaker ridge north of Dean...with a motion that is slower and a little to the right of previous forecasts. Given the initial motion...the first 12 hr of the forecast track will be essentially unchanged from the previous package...with a slight nudge to the right from 12-72 hr. After 72 hr...the forecast is becoming more problematic due to uncertainties in the eventual interaction of Dean and the upper-level low forecast to be over the Gulf of Mexico. The GFDL and UKMET models now call for Dean to turn northwestward into the central Gulf...while the Canadian...NOGAPS...and European models continue to forecast a westward motion across the Yucatan Peninsula into the Bay of Campeche. The GFS and the various consensus models are between these two extremes. The forecast track after 72 hr is also nudged a little to the right in agreement with the consensus guidance. The development of Dean has apparently been slowed by a combination of dry air intrusion in the western semicircle and light westerly shear. These conditions may persist for another 12-24 hr...so the intensity forecast calls for slow strengthening during this time. After 24 hr...conditions should be favorable for significant strengthening...with most of the intensity guidance calling for Dean to reach at least category 4 strength. The intensity forecast is the same as in the earlier advisory through 72 hr...then slightly stronger thereafter. It should be noted that the weakening from 96 to 120 hr is based on Dean crossing the Yucatan Peninsula...and if it instead moves through the Yucatan Channel it could remain stronger. Forecast positions and Max winds initial 17/0900z 14.3n 60.9w 85 kt 12hr VT 17/1800z 14.7n 63.6w 90 kt 24hr VT 18/0600z 15.3n 67.0w 95 kt 36hr VT 18/1800z 16.1n 70.5w 105 kt 48hr VT 19/0600z 16.9n 74.0w 115 kt 72hr VT 20/0600z 18.5n 81.0w 120 kt 96hr VT 21/0600z 20.5n 87.0w 125 kt 120hr VT 22/0600z 23.0n 92.0w 95 kt $$ forecaster Beven
Please, no more “nudges to the right”!
Things could get quite interesting by this time next week for those of us on the Texas gulf coast.
Not good.
The development of Dean has apparently been slowed by a combination of dry air intrusion in the western semicircle and light westerly shear. These conditions may persist for another 12-24 hr...so the intensity forecast calls for slow strengthening during this time.
Dean is already looking like the dry air's impact is lessening.