Tropical weather analysis - October 1, 2012
Nadine has weakened back to a tropical storm again. As of the latest NHC advisory, the following information was available on the storm:
Wind: 65 mph, with higher gusts
Location: 34.8°N 39.1°W
Movement: SSE at 9 mph
Pressure: 995 mb
Deep convection is limited to a band in the northern semicircle. The southern half of the circulation appears to have entrained some drier air.
Figure 1. Latest infrared satellite image of Tropical Storm Nadine. Image credit: RAMMB Colorado State University (CSU).
Nadine appears to be getting impacted by northwesterly shear, as evidenced by high cloud vectors on satellite images. A further increase in shear is forecast as the upper flow turns more northerly. In about 72 hours, an increase in southwesterly shear is forecast to impact Nadine. Assuming it has not dissipated by that time, that should surely deal the coup de grace. Nadine is expected to move across very cold water beyond 36 hours. It is possible that Nadine could become extratropical sooner than indicated below. Most of the global models show the circulation getting absorbed into a large low pressure amplifying off the eastern United States in the 72-96 timeframe.
Nadine is located between a deep-layer trough amplifying to the west, and a strong ridge to the east. This combination is expected to cause the tropical storm to turn eastward soon, followed by northeastward and then north. The models are in excellent agreement on the track, and it finally appears that Nadine has plans to exit the stage.
5-day intensity forecast
INITIAL 10/01 2100Z 55 KT 65 MPH
12 hour 10/02 0600Z 50 KT 60 MPH
24 hour 10/02 1800Z 45 KT 50 MPH
36 hour 10/03 0600Z 40 KT 45 MPH
48 hour 10/03 1800Z 40 KT 45 MPH
72 hour 10/04 1800Z 40 KT 45 MPH...POST-TROPICAL/EXTRATROPICAL
96 hour 10/05 1800Z...ABSORBED BY NORTH ATLANTIC LOW
5-day track forecast
Figure 2. My 5-day forecast track for Nadine.
A vigorous tropical wave in the eastern Atlantic is centered about 750 miles southwest of the Cape Verde Islands. Data from UW-CIMSS suggest that an anticyclone is beginning to build over the disturbance, which suggests an upper tropospheric wind pattern that is conducive to intensification. Indeed, the GFS shows a very favorable environment ahead of the system for the next few days. Beyond that time, there is some dichotomy between the GFS and the SHIPS beyond the 72 hour point; the former shows 96L abruptly losing its upper support as southwesterly shear increases, while the latter shows a very favorable environment and makes the system a major hurricane in 120 hours. This was as of 18z; I am still waiting for the 0z run, which should be out momentarily.
Environmental conditions favor the formation of a tropical depression over the next day or two as the wave moves west-northwest at 15 to 20 mph.
Probability of development in 48 hours: 60%