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Hurricane ISELLE Forecast Discussion Number 6
2014-08-02 04:38:56| National Hurricane Center (East Pacific)
Issued at 800 PM PDT FRI AUG 01 2014 000 WTPZ44 KNHC 020238 TCDEP4 HURRICANE ISELLE DISCUSSION NUMBER 6 NWS NATIONAL HURRICANE CENTER MIAMI FL EP092014 800 PM PDT FRI AUG 01 2014 Iselle's cloud pattern has increased in organization since the last advisory, transitioning from a banding to an eye pattern. Cloud top temperatures have also generally cooled in a small central dense overcast that has recently formed. Though ragged and occasionally obscured by high clouds, the 20 to 25 n mi diameter eye appeared well defined in an earlier AMSR-2 microwave overpass. Satellite intensity estimates were 3.5 and 4.0 from TAFB and SAB at 0000 UTC, respectively, with the latest ADT CI values at 4.0. Based on these data, the initial intensity is raised to 65 kt. The initial motion estimate is 295/10. Iselle should move steadily west-northwestward on the south side of a subtropical ridge until a mid- to upper-level trough digging along 130W in 2-3 days causes the ridge to weaken. Only a modest decrease in forward speed is expected in at that time before the ridge re-strengthens over the central Pacific by day 4, resulting in Iselle's moving faster toward the west. The track guidance is tightly clustered through 2 days but diverges some after that time, with the guidance shifting noticeably to the south at later times this cycle. The official track has been nudged a bit south in the short term and southward even more by days 3-5, but is not as far south as the multi-model consensus TVCE. Iselle is likely to continue to intensify during the next day or two. The closed low-level ring of convection in microwave imagery could portend a period of rapid intensification in the short term. However, moderate north-northeasterly shear and marginal thermodynamic parameters suggest this to be a lower probability scenario. After about 2 days, sea surface temperature drop below 26.5C and the environment is expected to gradually become even drier and more stable later in the forecast period. The shear could also increase substantially by days 4-5 in association with an upper-level trough, but this will depend on how far north Iselle tracks. The intensity forecast is higher than the previous one through about 2 days but is unchanged at later times, representing a blend of the multi-model consensus and the FSU Superensemble output. FORECAST POSITIONS AND MAX WINDS INIT 02/0300Z 14.7N 127.3W 65 KT 75 MPH 12H 02/1200Z 15.1N 128.7W 70 KT 80 MPH 24H 03/0000Z 15.5N 130.4W 75 KT 85 MPH 36H 03/1200Z 15.8N 132.3W 75 KT 85 MPH 48H 04/0000Z 16.2N 134.1W 75 KT 85 MPH 72H 05/0000Z 16.4N 137.0W 65 KT 75 MPH 96H 06/0000Z 16.5N 139.8W 60 KT 70 MPH 120H 07/0000Z 17.0N 144.5W 50 KT 60 MPH $$ Forecaster Kimberlain
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