Tropical weather analysis - July 6, 2012
Daniel
Tropical Storm Daniel is intensifying. As of the most recent NHC advisory, the following was posted:
Wind: 65 mph, with higher gusts
Location: 14.4°N 113.1°W
Movement: W at 13 mph
Pressure: 995 mb
Category: Tropical storm (Saffir-Simpson Hurricane Scale)
The cloud pattern hasn't changed significantly since the release of the advisory from the National Hurricane Center, although there appears to be more banding in the northern semicircle. Upper-tropospheric outflow is well-defined, except somewhat restricted to the south.
Figure 1. Latest infrared satellite image of Tropical Storm Daniel. Image credit: NOAA
Daniel has about another 24-36 hours under warm water temperatures before it begins to encounter the 26C isotherm. Although the cyclone is expected to remain embedded within a light shear environment throughout the next several days, water vapor imagery suggests that a large mass of dry air awaits Daniel west of 120W, likely associated with cooler waters. The result should be weakening, but not before Daniel becomes a hurricane. There is some suggestion by the GFS that northwesterly to westerly shear could increase across the system by Monday evening, as the tropical cyclone approaches the mid-oceanic trough in the vicinity of Hawaiian Islands. Although Daniel is expected to cross into the Central Pacific, it is unlikely to be a significant tropical cyclone when it reaches the longitude and/or latitude of Hawaii. However, interests there should still monitor it until its final progress can be determined.
Daniel is under the influence of a ridge to the north. This ridge has strengthened yesterday, just as the global models said it would. A continuation of a west to west-northwest motion is expected throughout the forecast period. The tropical storm is expected to cross 140°W longitude and enter the Central Pacific Hurricane Center (CPHC)'s area of responsibility late Tuesday or early Wednesday eastern time. Upon examining the global model fields, all of them are indicating a 500 mb weakness over and just north of the islands, in association with a weak cyclonic vorticity lobe, probably a portion of the mid-oceanic trough, a semipermanent feature of this basin. However, this weakness is not evident in the bottom half of the troposphere. Since Daniel is expected to be a weak system by that time, it will presumably respond to lower-tropospheric steering as opposed to mid-level steering. But things can change. Currently Daniel doesn't pose a direct threat to the Hawaiian Islands, but I will be monitoring synoptic trends in future forecasts.
5-day intensity forecast
INITIAL 07/06 0300Z 55 KT 65 MPH
12 hour 07/06 1200Z 65 KT 75 MPH
24 hour 07/07 0000Z 75 KT 85 MPH
36 hour 07/07 1200Z 80 KT 90 MPH
48 hour 07/08 0000Z 70 KT 80 MPH
72 hour 07/09 0000Z 55 KT 65 MPH
96 hour 07/10 0000Z 40 KT 45 MPH
120 hour 07/11 0000Z 30 KT 35 MPH
5-day track forecast
Figure 2. My 5-day forecast track for Daniel.
Gulf of Tehuantepec disturbance
A broad area of low pressure located several hundred miles south-southeast of the Gulf of Tehuantepec is producing disorganized showers and thunderstorms. Upper-level winds are favorable for slow development of this system over the next several days as it moves generally westward. Global models eventually develop this system into a hurricane following the same trajectory as Daniel.
Probability of development in 48 hours: 20%
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