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Tropical Storm ISELLE Forecast Discussion Number 4
2014-08-01 16:34:30| National Hurricane Center (East Pacific)
Issued at 800 AM PDT FRI AUG 01 2014 000 WTPZ44 KNHC 011434 TCDEP4 TROPICAL STORM ISELLE DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL EP092014 800 AM PDT FRI AUG 01 2014 Recent microwave data indicate that Iselle has a well-defined structure with a nearly closed ring of deep convection around the center. In infrared satellite imagery, hints of a possible ragged eye have been noted although the convection is a little thin on the western side. Dvorak intensity estimates are T2.5/35 kt from SAB, T3.5/55 kt from TAFB, and T3.9/63 kt from the UW-CIMSS ADT. The initial intensity is raised to 55 kt based on a blend of these data. The subtropical ridge continues to propel Iselle west-northwestward with an estimated motion of 295/9 kt. This motion is expected to continue for the next 48 hours. By day 3, however, a mid- to upper- level trough is forecast to amplify off the California coast while a fairly strong mid-level high becomes established just to the northeast of Hawaii. This pattern should cause Iselle to move more slowly toward the west between days 3 through 5. The track guidance is in good agreement for the first 2 days of the forecast but then diverges a bit thereafter, with the GFS and HWRF taking Iselle on a more northern trajectory and the ECMWF and GFDL staying farther to the south. The NHC official track forecast is largely unchanged from the previous advisory and remains near the multi-model consensus TVCE. UW-CIMSS shear analyses indicate that about 10 kt of northerly shear is affecting Iselle, which could be contributing to the thin convection on the western side. The shear is expected to change little for the next 24 hours but should then decrease thereafter. The thermodynamic environment will become a little more marginal in 2-3 days when Iselle approaches the 26C sea surface temperature isotherm and slightly more stable air. Therefore, Iselle is likely to peak in intensity in the next 36-48 hours and then gradually weaken on days 3-5. The intensity models have come into much better agreement compared to yesterday, and no significant changes were required to the official intensity forecast. FORECAST POSITIONS AND MAX WINDS INIT 01/1500Z 14.1N 125.7W 55 KT 65 MPH 12H 02/0000Z 14.6N 126.9W 65 KT 75 MPH 24H 02/1200Z 15.1N 128.6W 70 KT 80 MPH 36H 03/0000Z 15.5N 130.4W 75 KT 85 MPH 48H 03/1200Z 15.9N 132.2W 75 KT 85 MPH 72H 04/1200Z 16.5N 135.5W 70 KT 80 MPH 96H 05/1200Z 16.5N 138.0W 60 KT 70 MPH 120H 06/1200Z 17.0N 141.5W 50 KT 60 MPH $$ Forecaster Berg
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