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Tropical Storm Lee Forecast Discussion Number 22
2017-09-23 22:36:18| National Hurricane Center (Atlantic)
Issued at 500 PM AST Sat Sep 23 2017 000 WTNT44 KNHC 232036 TCDAT4 Tropical Storm Lee Discussion Number 22 NWS National Hurricane Center Miami FL AL142017 500 PM AST Sat Sep 23 2017 Compact Lee continues to produce a small cluster of central deep convection, along with several small curved bands in all quadrants. Ship LAOX5 traversed through the center of Lee around 1400Z, and at 1500Z reported a north wind of 30 kt about 20 nmi west of the center. Based on that ship observation, along with satellite intensity estimates of T2.5/35 kt from TAFB and UW-CIMSS ADT, the initial intensity remains at 40 kt for this advisory. The initial motion is a slow drift toward the north-northwest or 335/03 kt. The global and regional models have come into much better agreement on this cycle and now show a much tighter anticyclonic loop occurring during the forecast period, similar to the current and previous runs of the ECMWF model. As result, the official NHC forecast is west of the previous advisory track, and lies close to a blend of the TCVA, TVCX, and HCCA consensus models. There is no significant change to the previous forecast or reasoning. Due to the tighter loop that Lee is expected to make within the col region between an upper-level low to the south and a mid-latitude trough to the north, the deep-layer vertical wind shear is now forecast to remain less than 10 kt throughout the forecast period. Since the small cyclone will remain over SSTs near 27.5 C within a region of below-average upper-level temperatures, strong instability should persist for the next 4 days. The only inhibiting factor during that time will continue to be occasional intrusions of very dry mid-level air that will temporarily disrupt the inner-core convection. By 120 hours, gradual weakening is expected to begin due to increasing westerly shear. The new NHC intensity forecast is unchanged from the previous advisory, and remains close to a blend of the IVCN and HCCA intensity consensus models. FORECAST POSITIONS AND MAX WINDS INIT 23/2100Z 32.1N 49.8W 40 KT 45 MPH 12H 24/0600Z 32.3N 49.3W 45 KT 50 MPH 24H 24/1800Z 32.2N 48.7W 50 KT 60 MPH 36H 25/0600Z 31.8N 48.4W 55 KT 65 MPH 48H 25/1800Z 31.1N 48.2W 60 KT 70 MPH 72H 26/1800Z 30.5N 49.0W 70 KT 80 MPH 96H 27/1800Z 31.0N 50.5W 70 KT 80 MPH 120H 28/1800Z 32.4N 51.7W 65 KT 75 MPH $$ Forecaster Stewart
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