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Tropical Storm Isaac Forecast Discussion Number 26
2018-09-14 04:37:24| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Thu Sep 13 2018 073 WTNT44 KNHC 140237 TCDAT4 Tropical Storm Isaac Discussion Number 26 NWS National Hurricane Center Miami FL AL092018 1100 PM AST Thu Sep 13 2018 A burst of deep convection has developed and covered the previously exposed center of Isaac this evening. However, there is still evidence of northwesterly shear over the cyclone as there is a rather sharp edge to the convective mass and the cirrus is quickly blowing off toward the southeast. A recent ASCAT pass shows that the circulation is not particularly well defined, but it did show some light west or west-southwesterly winds, enough to keep the system classified as a tropical cyclone. The ASCAT also revealed winds of 30-32 kt, so the initial wind speed is held at 35 kt, which is also an average of the latest Dvorak current intensity numbers. Moderate to strong northwesterly shear and dry mid-level air are likely to cause Isaac to weaken to a tropical depression or even become an open wave within the next day or so. When Isaac reaches the west-central Caribbean Sea in a couple of days, the shear may relax somewhat and the global models suggest that there will be an increase in mid-level moisture. These conditions could allow for regeneration of the system, but given the uncertainty in whether Isaac will survive long enough to take advantage of these conditions, the official forecast still calls for dissipation like most of the guidance. Isaac continues moving westward at about 14 kt. The system should move generally westward over the next couple of days as it is steered by a low- to mid-level ridge to the north. Later in the period, the models show that Isaac could gain some latitude, but the official forecast is along the southern side of the guidance since a weaker system is likely to move more westward. The new NHC track forecast is essentially an update of the previous advisory. FORECAST POSITIONS AND MAX WINDS INIT 14/0300Z 14.9N 64.4W 35 KT 40 MPH 12H 14/1200Z 15.0N 66.5W 35 KT 40 MPH 24H 15/0000Z 15.0N 69.1W 30 KT 35 MPH 36H 15/1200Z 15.0N 71.4W 30 KT 35 MPH 48H 16/0000Z 15.2N 73.3W 30 KT 35 MPH 72H 17/0000Z 16.3N 77.5W 30 KT 35 MPH 96H 18/0000Z 17.7N 82.0W 30 KT 35 MPH 120H 19/0000Z...DISSIPATED $$ Forecaster Brown
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