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Tropical Storm ISELLE Forecast Discussion Number 5
2014-08-01 22:34:27| National Hurricane Center (East Pacific)
Issued at 200 PM PDT FRI AUG 01 2014 000 WTPZ44 KNHC 012034 TCDEP4 TROPICAL STORM ISELLE DISCUSSION NUMBER 5 NWS NATIONAL HURRICANE CENTER MIAMI FL EP092014 200 PM PDT FRI AUG 01 2014 Iselle has a well-defined structure in visible imagery and at times seems to have been trying to form an eye. However, the convective pattern as observed in infrared satellite imagery has been a little ragged and not as well structured. Dvorak estimates from TAFB and SAB are now unanimously T3.5/55 kt, but final-T estimates from the UW-CIMSS ADT have actually dropped to T3.1/47 kt since this morning. Based on these numbers, as well as a 50-kt estimate from a recent ASCAT-B pass, the initial intensity is held at 55 kt. The strengthening trend may be taking a temporary respite, but environmental conditions should support further intensification during the next 2-3 days. Modest northerly shear appears to be impinging on the storm, but that shear is expected to diminish in a day or two. By that time, thermodynamic conditions will become a little more marginal as Iselle approaches the 26C sea surface temperature isotherm. The intensity models are in fairly good agreement in showing modest strengthening, although the peak intensities have decreased a bit. Based on the latest guidance, the updated NHC intensity forecast shows Iselle reaching a maximum intensity of 70 kt in 36-48 hours. The track models are also in good agreement, showing very little spread during the first 3 days. The subtropical ridge to the north of Iselle should keep the cyclone on a west-northwestward track during that time. Iselle's forward speed is then expected to slow down on days 3 and 4 as it gets impeded by a mid-level ridge near Hawaii, and then speed up again on day 5 when the ridge slides eastward. No significant changes were required to the official track forecast, and the NHC points continue to lie very close the model consensus TVCE. FORECAST POSITIONS AND MAX WINDS INIT 01/2100Z 14.5N 126.4W 55 KT 65 MPH 12H 02/0600Z 14.9N 127.7W 60 KT 70 MPH 24H 02/1800Z 15.4N 129.5W 65 KT 75 MPH 36H 03/0600Z 15.9N 131.3W 70 KT 80 MPH 48H 03/1800Z 16.3N 133.2W 70 KT 80 MPH 72H 04/1800Z 16.6N 136.3W 65 KT 75 MPH 96H 05/1800Z 16.9N 138.7W 60 KT 70 MPH 120H 06/1800Z 17.5N 143.0W 50 KT 60 MPH $$ Forecaster Berg
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