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Tropical Depression Nineteen Forecast Discussion Number 1
2017-11-06 09:49:33| National Hurricane Center (Atlantic)
Issued at 500 AM AST Mon Nov 06 2017 000 WTNT44 KNHC 060849 TCDAT4 Tropical Depression Nineteen Discussion Number 1 NWS National Hurricane Center Miami FL AL192017 500 AM AST Mon Nov 06 2017 GOES-16 night-time visible and infrared satellite imagery indicate that convection associated with the well-defined low pressure system located over the central Atlantic Ocean has increased and become better organized during the past several hours. Satellite intensity estimates were T1.5/25 kt from both TAFB and SAB at 0600Z. Since that time, however, a burst of deep convection has developed over the previously partially exposed low-level circulation center, which had been located near the northwestern edge of the large convective cloud mass. Given that the center is now located farther into the deep convection, NHC objective intensity estimates have increased to more than 30 kt. As a result, advisories have been initiated on the nineteenth tropical depression of the 2017 Atlantic hurricane season. The initial motion estimate is 095/05 kt. The center of the cyclone has been moving slowly eastward within the larger cyclonic gyre for the past 12-18 hours, most likely due to the deep convection being sheared toward the east. However, the latest NHC model guidance indicates that the recent eastward motion should be short-lived since the larger gyre is forecast to begin moving northward within the next 6 h or so. As the wind field contracts over the next 24 hours, the motion of the cyclone should stabilize and become less erratic as deep-layer southerly steering flow becomes established on the west side of a large-scale subtropical ridge. By 48 h and beyond, southwesterly flow ahead of mid-latitude trough is forecast to accelerate the system toward the northeast through 96 h. By 120 h, the cyclone should have merged with a frontal system or have dissipated over the cold waters of the far north Atlantic. The official track forecast lies close to a blend of the TVCN, TVCX, and GFEX consensus track models. The cyclone is currently embedded within a low-shear environment in the col region between a weakening upper-level low located to the southeast and a trough to the northwest. The vertical wind shear is forecast by the GFS and ECMWF models to remain relatively low for the next 36 h or so, which should allow for some modest strengthening to occur despite sea-surface temperatures only being around 25-26 deg C. Temperatures of 2-3 deg C colder-than-normal in the mid- and upper-levels of the troposphere, however, should act to offset the cooler SSTs, providing sufficient instability to allow for deep convection to continue to develop. Model soundings and the FSU Cyclone Phase-Space diagram indicate that extratropical transition should begin shortly after 48 h when the cyclone reaches about 40N latitude and moves over much cooler water. The NHC intensity closely follows the HCCA and IVCN consensus models. FORECAST POSITIONS AND MAX WINDS INIT 06/0900Z 28.9N 50.2W 30 KT 35 MPH 12H 06/1800Z 30.0N 49.9W 35 KT 40 MPH 24H 07/0600Z 32.0N 49.6W 40 KT 45 MPH 36H 07/1800Z 35.4N 49.4W 45 KT 50 MPH 48H 08/0600Z 39.4N 48.2W 45 KT 50 MPH 72H 09/0600Z 49.0N 38.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 96H 10/0600Z 59.0N 15.0W 40 KT 45 MPH...POST-TROP/EXTRATROP 120H 11/0600Z...DISSIPATED $$ Forecaster Stewart
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