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Tropical Depression Kate Forecast Discussion Number 17
2021-09-01 10:33:59| National Hurricane Center (Atlantic)
Issued at 500 AM AST Wed Sep 01 2021 000 WTNT45 KNHC 010833 TCDAT5 Tropical Depression Kate Discussion Number 17 NWS National Hurricane Center Miami FL AL102021 500 AM AST Wed Sep 01 2021 After the earlier convective hiatus, a concentrated area of thunderstorm activity containing numerous lightning strikes has developed over and to the east of the low-level center. In addition, upper-level outflow has been expanding to the west, an indication that the hostile shear conditions that have been plaguing the cyclone the past few days has finally waned. ASCAT data around 0000-0100Z showed peak winds near 25 kt; however, the recent sharp increase in deep convection along with a consensus Dvorak subjective intensity of T2.0/30 kt supports increasing the intensity to 30 kt. The 30-kt advisory intensity is also supported by UW-CIMSS objective intensity estimates of T2.1/31 kt from ADT and 39 kt from SATCON. The initial motion estimate is 340/08 kt. Kate is moving north-northwestward between a small mid- to upper-level low to the south of the cyclone and deep-layer ridge located to the north and east of the system. A gradual turn toward the northwest is expected later today, followed by a turn back toward the north on Thursday as Kate rounds the western periphery of the ridge. By Friday, recurvature toward the north-northeast and northeast into the mid-latitude westerlies is forecast when the cyclone will be lifted out by an eastward-moving deep-layer trough currently crossing the western Atlantic. The new NHC track forecast is similar to but a little to the left of the previous advisory track, and closely follows the tightly packed consensus track forecast models TVCA and NOAA-HCCA. A 0505 UTC AMSR-2 microwave pass revealed that Kate's compact circulation had tightened up considerably since the earlier 0100 UTC ASCAT wind data, which shows a broad and elongated inner-core wind field. Also, Kate is currently passing between two small upper-level lows to the north and south of the cyclone, which is aiding the upper-level divergence across the system, albeit somewhat constrained due to the short distance of only about 300 nmi between the two upper lows. Given the locally enhanced outflow and the recent increase in deep convection, it s not out of the question that Kate could restrengthen back into a low-end tropical storm during the next 24 hours or so. However, the entrainment of dry mid-level air with humidity values less than 50 percent should prevent any significant or rapid restrengthening from occuring. by 48 hours, moderate northerly shear and even drier mid-level air should cause convection weaken, resulting in a gradual spin down of the circulation and eventual dissipation by 72 hours. The new NHC intensity forecast is similar to but slightly lower than the consensus intensity models IVCN and HCCA, and the Decay-SHIPS statistical-dynamical intensity model. FORECAST POSITIONS AND MAX WINDS INIT 01/0900Z 25.7N 51.7W 30 KT 35 MPH 12H 01/1800Z 26.9N 52.5W 30 KT 35 MPH 24H 02/0600Z 28.5N 53.2W 30 KT 35 MPH 36H 02/1800Z 30.3N 53.7W 25 KT 30 MPH 48H 03/0600Z 31.9N 53.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 60H 03/1800Z 33.5N 53.1W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 04/0600Z...DISSIPATED $$ Forecaster Stewart
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