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Tropical weather analysis - November 3, 2012

By: KoritheMan , 5:07 AM GMT on November 03, 2012


Wind: 45 mph, with higher gusts
Location: 12.7°N 119.4°W
Movement: WSW at 5 mph
Pressure: 1005 mb

After becoming completely exposed earlier in the day, a burst of deep convection has developed over the northeastern portion of the circulation. Satellite estimates support an initial intensity of 40 kt, and a 0200 UTC OSCAT pass indicated a large area of 30 kt wind vectors outside the deepest convection. Thus, it is reasonable to assume that stronger winds are probably occurring in lieu of the recent convective burst.

Figure 1. Latest infrared satellite image of Tropical Storm Rosa. Image credit: NOAA

Westerly shear is still affecting Rosa, and it appears to be slowly increasing. Thus, the cyclone is forecast to progressively weaken subsequent to this point, although the intensity was held at 40 kt for the first 12 hours due to the possibility of an expansion/persistence of the ongoing convective burst during the upcoming diurnal convective maximum period overnight tonight. The SHIPS and GFS continue to suggest that this shear will increase to over 30 kt in about 24 hours, which is coincidentally when the tropical storm is expected to weaken at a somewhat quicker rate. Remnant low status is shown at day two, followed by dissipation at day four.

Satellite fixes suggest that Rosa has turned toward the west this evening, although it may be hesitating again. The presumed slower motion could be a symptom of the convective resurgence, as the low-level center attempts to tuck underneath the thunderstorms. It is my expectation that this will be the general motif for the next 6-12 hours, so little movement is indicated at that time. Thereafter, Rosa is forecast to gradually accelerate as the surrounding steering currents strengthen due to an amplifying mid- to upper-level trough to the north of the tropical cyclone. However, water vapor imagery suggests that this trough is fairly weak, and should this continue, Rosa could track farther westward than forecast, particularly at longer ranges.

I have little apparent reason to disagree with the National Hurricane Center forecast track, and the track I signify below is a reflector of that.

5-day intensity forecast

INITIAL 11/03 0300Z 40 KT 45 MPH
12 hour 11/03 1200Z 40 KT 45 MPH
24 hour 11/04 0000Z 35 KT 40 MPH
36 hour 11/04 1200Z 30 KT 35 MPH
48 hour 11/05 0000Z 25 KT 30 MPH...POST-TROPICAL/REMNANT LOW
72 hour 11/06 0000Z 20 KT 25 MPH...POST-TROPICAL/REMNANT LOW
96 hour 11/07 0000Z...DISSIPATED

5-day track forecast

Figure 2. My 5-day forecast track for Rosa.

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

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Basement-dwelling pseudo-otaku with a thrill for forecasting on the side.

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