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Hurricane ISELLE Forecast Discussion Number 14
2014-08-04 04:48:36| National Hurricane Center (East Pacific)
Issued at 800 PM PDT SUN AUG 03 2014 000 WTPZ44 KNHC 040248 TCDEP4 HURRICANE ISELLE DISCUSSION NUMBER 14 NWS NATIONAL HURRICANE CENTER MIAMI FL EP092014 800 PM PDT SUN AUG 03 2014 Iselle's satellite appearance has essentially been steady state since the last advisory. The cyclone continues to exhibit many of the characteristics of an annular hurricane, with a nearly axisymmetric convective structure and a curious lack of convective features outside the well-defined cental dense overcast. A circular but cloud-filled 20-25 n mi wide eye is also evident in last-light visible imagery. The initial intensity is reduced only slightly to 95 kt in accordance with the latest CI numbers from TAFB and SAB. The initial motion estimate is a steady 280/10, with perhaps more of a due-west wobble during the last couple of hours. A mid-latitude trough extending southwestward along 130w is forecast to weaken the subtropical ridge north of Iselle during the next 24 hours. The effect of the weakened ridge should be a decrease in the cyclone's forward motion for a brief period during the next day or two as it approaches 140w. By day 3, the cyclone should find itself south of a newly established central Pacific ridge, which should steer Iselle west-northwestward at a considerably faster forward speed by days 4-5. The track forecast is little changed from the previous one and is in the middle of the guidance envelope, very close to the multi-model consensus TVCE. Even though Iselle is moving over marginally warm sea surface temperatures, its current annular structure in a very light-shear environment suggests that the cyclone might retain a higher intensity than the guidance might suggest if the large-scale environmental conditions do not vary much at least during the next day or possibly two. After that, significantly less favorable thermodynamic factors, such as increasingly drier and more stable air and water temperatures just below 26C, should result in weakening while Iselle nears the Hawaiian Islands. An accelerated weakening may take place as Iselle makes its closest approach to the Hawaiian chain when environmental conditions become even more hostile. The intensity forecast is about the same as the previous one and is near the multi-model consensus IVCN and the SHIPS/LGEM output. FORECAST POSITIONS AND MAX WINDS INIT 04/0300Z 15.9N 134.8W 95 KT 110 MPH 12H 04/1200Z 16.0N 136.2W 90 KT 105 MPH 24H 05/0000Z 16.0N 137.8W 85 KT 100 MPH 36H 05/1200Z 16.0N 139.3W 80 KT 90 MPH 48H 06/0000Z 16.5N 141.3W 75 KT 85 MPH 72H 07/0000Z 18.1N 146.8W 60 KT 70 MPH 96H 08/0000Z 20.1N 153.1W 45 KT 50 MPH 120H 09/0000Z 22.3N 159.2W 40 KT 45 MPH $$ Forecaster Kimberlain
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