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Tropical Storm IVETTE Forecast Discussion Number 10
2016-08-05 04:45:18| National Hurricane Center (East Pacific)
Issued at 800 PM PDT THU AUG 04 2016 000 WTPZ45 KNHC 050245 TCDEP5 TROPICAL STORM IVETTE DISCUSSION NUMBER 10 NWS NATIONAL HURRICANE CENTER MIAMI FL EP102016 800 PM PDT THU AUG 04 2016 Though it may sound like a broken record, Ivette still is struggling to intensify and is showing the detrimental effects of vertical shear. The low-level center appears to be on the northwest side of the small area of cold cloud tops, consistent with some west-northwesterly shear as shown in the SHIPS diagnostics and the CIMSS analyses. Yet, the deep-layer vertical shear is only 5-10 kt, which usually is conducive for intensification. Perhaps it is because of the small size of Ivette - tropical-storm-force winds only out to 60 nm at most - which makes it more susceptible to relatively small amounts of shear. A blend of the TAFB, SAB, and CIMSS Dvorak current intensity estimates gives 45 kt, which is unchanged from the previous advisory. An earlier ASCAT scatterometer pass confirmed the small size of Ivette. Ivette has about two days left to intensify under what appear to be conducive environmental conditions. After a couple days, the SSTs cool and the low-level moisture decreases, but still at levels that could support intensification. By days four and five, however, the vertical shear should reach at least 20 kt due to an upper-level trough approaching Ivette. Gradual to steady intensification is thus expected to about 36-48 hours with gradual to steady weakening thereafter. The NHC intensity forecast is closest to a blend of the SHIPS statistical technique and the COAMPS regional dynamical model and is slightly less than that predicted in the previous advisory. Given the poor intensity forecasts thus far, this prediction has a large uncertainty. Ivette is moving toward the west at 12 kt, primarily being steered by the deep-layer subtropical ridge extending westward out of Mexico. The tropical cyclone should begin bending toward the west-northwest in a couple days as it attempts to round the western periphery of the ridge. By day four or five, Ivette should turn back toward the west as the decaying system is advected in the low-level tradewind flow. All of the reliable models are in close agreement and the NHC track forecast - based upon the TVCN track consensus - is nearly unchanged. FORECAST POSITIONS AND MAX WINDS INIT 05/0300Z 14.8N 128.7W 45 KT 50 MPH 12H 05/1200Z 14.9N 130.3W 50 KT 60 MPH 24H 06/0000Z 15.3N 132.2W 55 KT 65 MPH 36H 06/1200Z 15.9N 134.0W 60 KT 70 MPH 48H 07/0000Z 16.6N 135.7W 60 KT 70 MPH 72H 08/0000Z 18.0N 138.6W 50 KT 60 MPH 96H 09/0000Z 18.7N 142.0W 40 KT 45 MPH 120H 10/0000Z 19.0N 146.0W 30 KT 35 MPH $$ Forecaster Landsea
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