ZCZC MIATCDEP4 ALL TTAA00 KNHC DDHHMM TROPICAL STORM ISELLE DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL EP092014 200 PM PDT THU JUL 31 2014 Deep convection has been wrapping up quickly during the past few hours near the low pressure system located near 122W, and TAFB and SAB have both provided Dvorak estimates of T2.0/30 kt. In addition, a partial 1800 UTC ASCAT-B pass indicated that the low is already producing winds to tropical storm force in the eastern semicircle. Therefore, advisories are being initiated on Tropical Storm Iselle, and the maximum winds are conservatively set at 35 kt. With sea surface temperatures ahead of Iselle running between 27-28C and vertical shear not expected to be a significant limiting factor, the storm is forecast to strengthen for at least the next 3 days. The strengthening rate could be quick for the next day or so, with the SHIPS rapid intensification index showing a 44 percent chance of a 25-kt increase in winds by this time tomorrow. The SHIPS guidance is the most aggressive of the intensity models and brings Iselle to hurricane status within the next 24-36 hours. The NHC official intensity forecast is not as high as the SHIPS model, but since the environment looks favorable for strengthening, it does lie a little above the intensity consensus ICON. Iselle is located to the south of a mid-level ridge which extends from northwestern Mexico southwestward to near 20N140W, and the cyclone's estimated initial motion is 295/9 kt. In general, ridging is expected to maintain a relatively steady west-northwestward motion for the next several days. Some slight decrease in forward speed is possible by day 4 when a weakness develops within the ridge near 135W and ridging strengthens near the Hawaiian Islands. The track guidance is tightly clustered for this forecast, and the NHC track forecast lies very close to the multi-model consensus TVCE. FORECAST POSITIONS AND MAX WINDS INIT 31/2100Z 12.7N 122.3W 35 KT 40 MPH 12H 01/0600Z 13.4N 123.5W 45 KT 50 MPH 24H 01/1800Z 14.2N 125.0W 55 KT 65 MPH 36H 02/0600Z 14.8N 126.7W 60 KT 70 MPH 48H 02/1800Z 15.1N 128.3W 65 KT 75 MPH 72H 03/1800Z 16.0N 132.0W 70 KT 80 MPH 96H 04/1800Z 16.0N 135.0W 65 KT 75 MPH 120H 05/1800Z 16.0N 138.0W 60 KT 70 MPH $$ Forecaster Berg NNNN
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Page last modified: Wednesday, 31-Dec-2014 12:09:35 UTC