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Tropical Storm Cosme Forecast Discussion Number 1
2019-07-06 16:03:14| National Hurricane Center (East Pacific)
Issued at 800 AM PDT Sat Jul 06 2019 720 WTPZ43 KNHC 061403 TCDEP3 Tropical Storm Cosme Discussion Number 1 NWS National Hurricane Center Miami FL EP032019 800 AM PDT Sat Jul 06 2019 The broad area of low pressure that we have been monitoring for several days has finally consolidated into a tropical storm. Satellite images show that a well-defined center is present on the western side of an area of deep convection which has been getting closer to the center. The initial wind speed is set to 45 kt in agreement with the overnight scatterometer data, which is higher than what Dvorak-only estimates would suggest. Shear near Cosme has been decreasing during the overnight hours, with cirrus cloud motions suggesting that easterly flow is overspreading the circulation. However, it will take some time for the large cyclone to overcome the very dry mid-level air near and west of the core. In addition, Cosme has only about 36 hours over lukewarm SSTs before reaching cool waters. These factors suggest little significant strengthening this weekend, and a gradual weakening early next week due to sub-26C waters and higher shear. Only the HWRF shows any significant increase in wind speed, with the rest of the models holding Cosme's intensity flat or decreasing during the next few days. The official intensity forecast goes with the latter solution, not too far from the model consensus. An uncertain estimate of initial motion is 290/12. Cosme should be steered to the west-northwest for the next day or so due to a subtropical ridge over Mexico. However all of the models show a break in the ridge forming between 120-130W, which will likely induce a motion more to the northwest by Monday. There isn't a lot of agreement, however, on exactly when that turns occurs, with the GFS-based guidance and UKMET turning the system the system earlier than the ECMWF and most of its ensemble. I don't have a lot of reason to favor either solution at this time, so the forecast will stay close to the eastern Pacific track model consensus TVCE. Based on SSTs and model-simulated satellite data, Cosme should become a non-convective remnant low in about 3 days. FORECAST POSITIONS AND MAX WINDS INIT 06/1500Z 15.6N 115.7W 45 KT 50 MPH 12H 07/0000Z 16.3N 117.4W 45 KT 50 MPH 24H 07/1200Z 17.0N 119.1W 45 KT 50 MPH 36H 08/0000Z 17.9N 120.3W 45 KT 50 MPH 48H 08/1200Z 18.8N 121.2W 40 KT 45 MPH 72H 09/1200Z 20.2N 122.8W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 10/1200Z 21.0N 125.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 11/1200Z...DISSIPATED $$ Forecaster Blake
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