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Tropical Storm VANCE Forecast Discussion Number 7
2014-10-31 21:55:29| National Hurricane Center (East Pacific)
Issued at 200 PM PDT FRI OCT 31 2014 000 WTPZ41 KNHC 312055 TCDEP1 TROPICAL STORM VANCE DISCUSSION NUMBER 7 NWS NATIONAL HURRICANE CENTER MIAMI FL EP212014 200 PM PDT FRI OCT 31 2014 Vance has a peculiar structure this afternoon. The central convection has become somewhat skeletal with the center exposed at times, although there are still plenty of curved banding features in the outer portion of the circulation. The culprit for this decrease in convection appears to be an influx of dry air moving into the central region of the tropical cyclone around the west and south sides. Dvorak estimates still support an intensity of about 40 kt. Since the dry air is close to the center now, it will probably take some time for this air to mix out. Thus little change is shown in the short term. Afterward, models insist that the large-scale environment will become favorable for strengthening over the next three days or so. Strong southwesterly shear is anticipated for the beginning of next week, which will probably cause Vance to weaken significantly at long range. There has not been much change to the guidance suite, with the majority of the guidance still showing Vance as a hurricane in a few days. The NHC forecast is therefore very close to the previous one, and generally lies between the intensity consensus and the SHIPS model. It seems that finally the motion of Vance has become more clear, now moving west-southwestward at about 6 kt. This general motion is expected through tonight due to a ridge over the eastern Pacific. This ridge should move eastward over the next few days, steering the cyclone more westward tomorrow, and to the northwest by late this weekend. Vance is then forecast to turn northward and then north- northeastward ahead of a trough moving over Baja California. Subtle differences in the speed of the trough are leading to increased model spread at long range, with the faster ECMWF preferring a more north-northeast track, compared to the slower GFS solution of a sharper northeastward turn. The NHC forecast is adjusted westward at day 3 and beyond, and is close to a dynamical model consensus excluding the UKMET model, which has an improbable forecast due to a seemingly spurious interaction with a weak ITCZ disturbance. FORECAST POSITIONS AND MAX WINDS INIT 31/2100Z 9.5N 101.4W 40 KT 45 MPH 12H 01/0600Z 9.3N 102.4W 40 KT 45 MPH 24H 01/1800Z 9.6N 104.1W 45 KT 50 MPH 36H 02/0600Z 10.5N 106.2W 55 KT 65 MPH 48H 02/1800Z 11.7N 108.4W 65 KT 75 MPH 72H 03/1800Z 16.0N 110.5W 70 KT 80 MPH 96H 04/1800Z 19.8N 108.5W 50 KT 60 MPH 120H 05/1800Z 23.5N 106.0W 30 KT 35 MPH...INLAND $$ Forecaster Blake
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