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Tropical Storm Lee Forecast Discussion Number 19
2017-09-23 04:52:46| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Fri Sep 22 2017 000 WTNT44 KNHC 230252 TCDAT4 Tropical Storm Lee Discussion Number 19 NWS National Hurricane Center Miami FL AL142017 1100 PM AST Fri Sep 22 2017 Several microwave overpasses between 2100 and 2200 UTC indicated that Lee was becoming better organized, at least at the mid-levels. In particular, a WindSat overpass near 21Z indicated that a mid-level eye was already forming. Since that time, however, cloud tops have warmed, the CDO has shrunk, and a GPM overpass around 0100 UTC showed that most of the convection is currently confined to the southeast semicircle of the tropical storm. The UW-CIMSS ADT supports an intensity of 35 kt, and the TAFB Dvorak analyst indicated that the subjective classification would have been higher, if the technique wasn't constrained by the fact that classifications on Lee only recently restarted. Based on these data, the initial intensity has been increased to 35 kt. The intensity forecast for Lee is highly uncertain. The tropical storm is very small, and small cyclones often quickly strengthen or weaken. Furthermore, Lee is small enough that some of our models (and many of our observing platforms) may have trouble resolving the inner core of the storm. Given the current convective state of Lee, significant strengthening in the short term seems unlikely. However, the cyclone is expected to be in a fairly unstable, low shear environment for at least the next 3 days, so it is possible that rapid intensification could occur at some time during that period. On the other hand, I can't rule out that the cyclone could dissipate entirely, as depicted by the GFS, within a couple days. For now, my forecast is closest to the HWRF for the first 72 h, since that model tends to do well in low-shear environments and should have sufficient resolution to model Lee's core. After that time, the forecast is close to the HCCA and IVCN intensity consensus models. Lee has continued to move north around 6 kt. Little change has been made to the track forecast, and Lee is still forecast to move around a subtropical ridge for the next 72 h. At days 4 and 5, a ridge building between Lee and Maria to the west should cause a turn more toward the south, as long as Lee is sufficiently deep to be steered by that feature. The forecast continues to be close to the ECMWF, since it is still the global model with the strongest representation of Lee, in line with the NHC forecast. FORECAST POSITIONS AND MAX WINDS INIT 23/0300Z 31.5N 49.0W 35 KT 40 MPH 12H 23/1200Z 32.2N 48.5W 40 KT 45 MPH 24H 24/0000Z 32.5N 47.8W 45 KT 50 MPH 36H 24/1200Z 32.4N 46.6W 50 KT 60 MPH 48H 25/0000Z 32.1N 45.2W 60 KT 70 MPH 72H 26/0000Z 31.3N 43.1W 75 KT 85 MPH 96H 27/0000Z 30.0N 42.5W 75 KT 85 MPH 120H 28/0000Z 29.5N 43.5W 65 KT 75 MPH $$ Forecaster Zelinsky
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