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Tropical Storm Gonzalo Forecast Discussion Number 4
2020-07-22 16:39:33| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Wed Jul 22 2020 000 WTNT42 KNHC 221439 TCDAT2 Tropical Storm Gonzalo Discussion Number 4 NWS National Hurricane Center Miami FL AL072020 1100 AM AST Wed Jul 22 2020 Satellite imagery indicates that the cyclone has become significantly better organized since the last advisory. Visible imagery shows a well-defined central dense overcast with a hint of an eye and an outer convective band in the western semicircle, while a 09Z GMI microwave overpass showed a well-defined inner convective ring feature. Various subjective and objective satellite intensity estimates range from 35-55 kt, so the initial intensity is raised to a possibly conservative 45 kt. The initial motion is now 270/10. Gonzalo is on the south side of a low- to mid-level subtropical ridge, and this feature should steer the storm generally westward at a faster forward speed for the next 3 days or so. After that time, a motion toward the west-northwest is expected. The new NHC forecast track is little changed from the previous track, and it lies very close to the consensus models. The intensity forecast remains very problematic and of low confidence. On one side, the cyclone has been strengthening quickly and the good organization suggests additional, and possibly rapid, strengthening should occur. In addition, the SHIPS-based guidance and the HWRF make the system a hurricane and keep that intensity through 120 h. On the other side, the GFS, UKMET, ECMWF, and Canadian models are not big fans of this system, as they all forecast it to either be a weak low or dissipated by 120 h, possibly due to dry air entrainment and large-scale subsidence. The NHC intensity forecast again compromises between these extremes, showing Gonzalo peaking as a hurricane in 36-48 h, followed by weakening in deference to the global models. The new intensity forecast has significantly higher intensities than the previous forecast for most of the forecast period based on the recent intensification. As noted before, the small size of this system makes it susceptible to significant fluctuations in intensity, both upward and downward. Interests in the southern Windward Islands should monitor the progress of this system. Gonzalo is the earliest 7th named storm on record in the Atlantic basin, beating Gert of 2005 by 2 days. Key Messages 1. Gonzalo is expected to move near or over the southern Windward Islands this weekend, and could bring direct impacts from winds and heavy rainfall. While it is too soon to determine the magnitude and timing of those impacts, interests in the southern Windward Islands should monitor the progress of Gonzalo. FORECAST POSITIONS AND MAX WINDS INIT 22/1500Z 9.9N 43.6W 45 KT 50 MPH 12H 23/0000Z 10.0N 45.3W 55 KT 65 MPH 24H 23/1200Z 10.0N 47.7W 65 KT 75 MPH 36H 24/0000Z 10.1N 50.2W 70 KT 80 MPH 48H 24/1200Z 10.4N 52.8W 70 KT 80 MPH 60H 25/0000Z 10.7N 55.6W 65 KT 75 MPH 72H 25/1200Z 11.4N 58.8W 60 KT 70 MPH 96H 26/1200Z 13.0N 66.0W 50 KT 60 MPH 120H 27/1200Z 15.0N 71.5W 40 KT 45 MPH $$ Forecaster Beven
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