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Tropical Storm IVETTE Forecast Discussion Number 6
2016-08-04 04:51:29| National Hurricane Center (East Pacific)
Issued at 800 PM PDT WED AUG 03 2016 000 WTPZ45 KNHC 040251 TCDEP5 TROPICAL STORM IVETTE DISCUSSION NUMBER 6 NWS NATIONAL HURRICANE CENTER MIAMI FL EP102016 800 PM PDT WED AUG 03 2016 Moderate northeasterly vertical shear continues to afflict Ivette, as the deep convection is asymmetric with most of the cold cloud tops southwest of the center. A blend of the TAFB and SAB subjective Dvorak, the CIMSS Advanced Dvorak, and AMSU estimates gives an intensity of 40 kt, unchanged from the previous advisory. A pair of ASCAT scatterometer passes around 18Z indicates that Ivette remains small sized, but slightly larger in tropical-storm-force wind radii than previously estimated. The scatterometer passes and an AMSR2 image at 2023Z suggested that Ivette's center was farther south than previously analyzed. This was confirmed by the brief appearance of the low-level center in geostationary visible imagery, as it peeked out from the edge of the deep convection. Ivette is moving toward the west at 14 kt, along the southern edge of a deep-layer subtropical ridge extending westward from Mexico. The tropical cyclone should continue moving toward the west or west-northwest at a slightly slower rate of forward speed for the next few days. The NHC track forecast is based upon the tightly clustered global and regional hurricane models, and is slightly south of the previous advisory because of the southward revision to the initial position. The continuing steady state of Ivette would argue for little change in the short term, but the global models insist that the vertical shear should be diminishing now. The NHC intensity forecast assumes that the shear will lower during the next two to three days while the SSTs are quite warm and the atmosphere is moist and unstable, leading to a steady intensification of Ivette. Beyond day three, the vertical shear should ramp up again out of the southwest as a large upper-level trough approaches Ivette while the SSTs cool, causing Ivette to gradually weaken. The NHC intensity forecast is based upon a blend of the SHIPS and HWRF models, and is slightly below that from the previous advisory. FORECAST POSITIONS AND MAX WINDS INIT 04/0300Z 14.6N 123.4W 40 KT 45 MPH 12H 04/1200Z 14.7N 125.5W 45 KT 50 MPH 24H 05/0000Z 14.9N 128.2W 50 KT 60 MPH 36H 05/1200Z 15.1N 130.5W 60 KT 70 MPH 48H 06/0000Z 15.5N 132.5W 70 KT 80 MPH 72H 07/0000Z 16.7N 136.3W 75 KT 85 MPH 96H 08/0000Z 18.0N 140.0W 65 KT 75 MPH 120H 09/0000Z 19.0N 143.0W 50 KT 60 MPH $$ Forecaster Landsea
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