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Hurricane ISELLE Forecast Discussion Number 9
2014-08-02 22:35:31| National Hurricane Center (East Pacific)
Issued at 200 PM PDT SAT AUG 02 2014 000 WTPZ44 KNHC 022035 TCDEP4 HURRICANE ISELLE DISCUSSION NUMBER 9 NWS NATIONAL HURRICANE CENTER MIAMI FL EP092014 200 PM PDT SAT AUG 02 2014 Despite continued north-northeasterly shear, Iselle has strengthened to category 2 strength during the past few hours. The deep convection remains a little asymmetric, favoring the eastern semicircle, but Dvorak estimates have still risen to T4.5/77 kt from TAFB and T5.0/90 kt from SAB and the UW-CIMSS ADT. These data, combined with an earlier AMSU estimate of 78 kt, support raising the initial intensity to 85 kt. The vertical shear, such as it is, is still expected to diminish during the next 12-24 hours. At the same time, Iselle will be moving over decreasing oceanic heat content values, and the stronger winds will likely lead to increased upwelling of colder water. The official forecast allows for a little more intensification in the short term, but after 24 hours the less favorable thermodynamic environment should induce gradual weakening. The updated NHC intensity forecast is a little bit higher than the previous one only during the first 3 days to account for the higher initial intensity. Beyond day 3, the GFDL and HWRF keep Iselle near the threshold of hurricane intensity while the statistical models show a more marked decrease in winds. The NHC intensity forecast is very close to the LGEM and FSU Superensemble on days 4 and 5. Iselle's initial motion is 280/8 kt. The hurricane is expected to maintain a general westward motion but could slow down a bit in 48-72 hours when the ridge to the north of Iselle weakens. By days 4 and 5, a mid-level high northeast of Hawaii is anticipated to strengthen and slide eastward, which should impart a faster westward motion at the end of the forecast period. The track guidance is tightly clustered during the first 72 hours, but most of the models, particularly the ECMWF and GFDL, have shifted northward on this cycle. The updated NHC track forecast is also nudged northward on days 4 and 5 and lies close to the FSU Superensemble. FORECAST POSITIONS AND MAX WINDS INIT 02/2100Z 15.1N 130.1W 85 KT 100 MPH 12H 03/0600Z 15.4N 131.5W 90 KT 105 MPH 24H 03/1800Z 15.7N 133.5W 90 KT 105 MPH 36H 04/0600Z 15.9N 135.4W 85 KT 100 MPH 48H 04/1800Z 16.0N 137.0W 80 KT 90 MPH 72H 05/1800Z 16.0N 140.0W 75 KT 85 MPH 96H 06/1800Z 16.5N 144.5W 60 KT 70 MPH 120H 07/1800Z 17.5N 150.5W 45 KT 50 MPH $$ Forecaster Berg
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