Tropical Development Likely Today

Weather

10:00 am National Hurricane Center update:

High-resolution satellite imagery along with surface and upper-air data indicate that the broad low pressure system located over the northeastern Gulf of Mexico has become a little better defined. The initial intensity of 25 kt is based on an average of 1-minute wind speeds of 20-33 kt reported by ships and buoys well south of the poorly defined center. Although the system is currently experiencing some northerly vertical wind shear, the shear is expected to gradually subside over the next day or so, and the low has a high chance of becoming a tropical depression or tropical storm by Thursday. Since this system has the potential to bring tropical storm conditions and storm surge to portions of the coast of Louisiana by late Thursday or Friday, Potential Tropical Cyclone advisories are being initiated at this time.

The initial motion estimate is an uncertain 245/07 kt. Some erratic motion will be possible during the 24 hours or until a well-defined center develops. However, the general motion as indicated by the global and regional models is expected to be toward the west-southwest or southwest. By Friday, the cyclone is forecast to turn toward the west-northwest and then turn northwestward by Saturday into a developing break in a deep-layer ridge that currently extends from the southeastern U.S. westward across the southern Plains and into the Desert Southwest. The timing of the ridge breakdown owing to a shortwave trough moving southeastward out of the northern Plains will be critical since a later/earlier turn by the cyclone would shift the track west/east of the current forecast. The model guidance is widely divergent after 48 hours with the UKMET model the farthest west showing landfall along the Upper Texas coast, and the

GFS and HMON models farther east with landfall in south-central

Louisiana. The ECMWF model is about midway between these two extremes, and the official track forecast leans toward that model since it has performed well during this system’s pre-development phase.  Note that forecast uncertainty for disturbances is generally larger than for tropical cyclones, especially beyond 48-72 hours.

Only slow strengthening is expected for the next 24-36 hours due to the lack of a well-defined center and inner-core wind field, along with some modest northerly wind shear. By 48 hours and beyond, however, the combination of atmospheric and oceanic conditions become ideal for intensification. The very low shear shear conditions, an impressive outflow pattern forecast by all of the global and regional models, and anomalously warm sea-surface temperatures of 30-31C argue for quick intensification, but given that the system is still in the formative stages, the official intensity forecast is a little below IVCN consensus through 48 hours and trends higher toward the ECMWF-based SHIPS guidance at 72 hours.

Key Messages:

1. A tropical depression is expected to form later today or Thursday. Conditions appear favorable for this system to strengthen to a hurricane at it approaches the central Gulf Coast by the weekend.

2. Dangerous storm surge is possible in portions of southeast

Louisiana, and a Storm Surge Watch has been issued for this area.

The risk for dangerous storm surge impacts also exists farther west along the Louisiana coast into the Upper Texas coast, and additional storm surge watches may be needed later today or tonight. Residents in these areas should monitor the progress of this system and listen to any advice given by local officials.

3. A Tropical Storm Watch has been issued for portions of the Louisiana coast and additional Tropical Storm or Hurricane Watches could be needed later today or tonight for the remainder of the Louisiana coast and the Upper Texas Coast.

4. The system has the potential to produce very heavy rainfall along and inland of the central Gulf Coast through early next week. For more information, see products from your local National Weather Service office and the NOAA Weather Prediction Center.

FORECAST POSITIONS AND MAX WINDS

INIT  10/1500Z 28.5N  86.4W   25 KT  30 MPH…POTENTIAL TROP CYCLONE

 12H  11/0000Z 27.9N  87.3W   25 KT  30 MPH…POTENTIAL TROP CYCLONE

 24H  11/1200Z 27.5N  88.2W   30 KT  35 MPH…TROPICAL DEPRESSION

 36H  12/0000Z 27.4N  89.3W   40 KT  45 MPH

 48H  12/1200Z 27.6N  90.4W   50 KT  60 MPH

 72H  13/1200Z 28.7N  92.3W   75 KT  85 MPH

 96H  14/1200Z 30.7N  93.0W   65 KT  75 MPH…INLAND

120H  15/1200Z 32.6N  94.1W   30 KT  35 MPH…INLAND

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