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Tropical Depression FOUR Forecast Discussion Number 3
2017-07-06 16:34:21| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Thu Jul 06 2017 000 WTNT44 KNHC 061434 TCDAT4 Tropical Depression Four Discussion Number 3 NWS National Hurricane Center Miami FL AL042017 1100 AM AST Thu Jul 06 2017 A series of microwave images, an earlier NRL WindSAT scatterometer overpass, and recent ASCAT-B surface wind retrievals indicate that the surface circulation of the depression has become less organized. The center remains near the eastern edge of an amorphous blob of deep convection and is a bit farther south than previously thought. Enhanced BD-curve infrared imagery also shows that the cloud tops have warmed considerably during the past 6 hours. The initial intensity is held at 25 kt for this advisory based on the deteriorating cloud pattern and a blend of the TAFB and SAB satellite intensity estimates. Large-scale dry, sinking air associated with a previous Saharan Air Layer outbreak continues to be the primary inhibiting factor affecting the cyclone. Global and ensemble guidance show the system degenerating into a remnant low or trough in 3 days or less, due to the aforementioned harsh thermodynamic environment and increasing moderate westerly shear. The official intensity forecast is basically an update of the previous advisory and favors the dynamical models. The initial motion is estimated to be west-northwestward, or 285/18 kt. The circulation center continues to be difficult to locate, but the above-mentioned scatterometer pass was helpful in obtaining the position estimate. The depression is forecast to be steered by the low- to mid-level flow associated with a building subtropical ridge situated to its north over the next several days. The new official forecast is about a half a degree south of the previous one due to the initial position adjustment. The NHC track is close to the latest TVCN multi-model consensus. FORECAST POSITIONS AND MAX WINDS INIT 06/1500Z 13.2N 42.6W 25 KT 30 MPH 12H 07/0000Z 14.0N 45.3W 30 KT 35 MPH 24H 07/1200Z 15.1N 49.3W 30 KT 35 MPH 36H 08/0000Z 16.2N 52.9W 30 KT 35 MPH 48H 08/1200Z 17.7N 56.6W 25 KT 30 MPH 72H 09/1200Z 20.6N 62.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 10/1200Z 23.0N 67.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 11/1200Z...DISSIPATED $$ Forecaster Roberts
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