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Tropical Storm IVETTE Forecast Discussion Number 14
2016-08-06 05:00:27| National Hurricane Center (East Pacific)
Issued at 800 PM PDT FRI AUG 05 2016 000 WTPZ45 KNHC 060300 TCDEP5 TROPICAL STORM IVETTE DISCUSSION NUMBER 14 NWS NATIONAL HURRICANE CENTER MIAMI FL EP102016 800 PM PDT FRI AUG 05 2016 The convective structure of Ivette has not changed substantially this evening with most of the convection limited to the northeastern semicircle. A blend of the TAFB/SAB Dvorak, CIMSS Advanced Dvorak, and AMSU intensity estimates indicate about 50 kt at the initial time, unchanged from the previous advisory. Ivette remains small in size, as indicated by the limited central dense overcast and tropical-storm-force wind radii from CIRA/AMSU. While Ivette remains over 28C water, the vertical shear appears to still be disrupting the convection, as the center - like yesterday - is occasionally showing up just west of the cirrus canopy. Even though the shear is quite low (5 to 10 kt from the CIMSS and SHIPS analyses), Ivette's small size and moderate intensity isn't enough to overcome the shear's detrimental effects. The tropical storm has about 12-24 hours of time left to intensify before the combination of cool SSTs, dry stable air, and strong southwesterly vertical shear kicks in. Once that combination begins, Ivette should steadily weaken and become a remnant low in about four days and dissipate shortly afterwards. The NHC intensity forecast, based upon the IVCN intensity consensus technique, indicates a slight intensification shortly before weakening commences in a couple days. It is of note that the only model to show significant strengthening - COAMPS, boosting Ivette to about 60 kt - has been the best performing guidance during the cyclone's lifetime. There have been several helpful microwave images of Ivette providing an accurate assessment of the system's center. These indicate that the tropical storm has not yet turned west-northwestward, as Ivette continues moving westward at 9 kt, due the steering influence of a mid-level subtropical ridge to its north. Despite the current motion, Ivette should turn toward the west-northwestward shortly, as it begins to round the western periphery of the ridge. However, in about three days, the tropical cyclone should bend back toward west as it is advected along in the easterly trade winds. The NHC track forecast is based upon the tightly clustered members of the multi-model ensemble (TVCN) and is somewhat south of the track from the previous advisory at 12 and 24 hours because of the unexpected continuation of westward motion. FORECAST POSITIONS AND MAX WINDS INIT 06/0300Z 15.4N 132.6W 50 KT 60 MPH 12H 06/1200Z 15.8N 134.0W 55 KT 65 MPH 24H 07/0000Z 16.6N 135.8W 55 KT 65 MPH 36H 07/1200Z 17.4N 137.5W 50 KT 60 MPH 48H 08/0000Z 18.2N 138.9W 40 KT 45 MPH 72H 09/0000Z 18.8N 141.8W 30 KT 35 MPH 96H 10/0000Z 18.5N 145.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 11/0000Z...DISSIPATED $$ Forecaster Landsea
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