Tropical weather analysis - May 24. 2012
Invest 94L
A broad area of disturbed weather over the western Caribbean Sea is producing widespread showers and thunderstorms east of the center. Although the associated convection is quite deep, the latest SHIPS model output and CIMSS analysis depict about 40 knots of westerly shear over the system.
Figure 1. Latest infrared satellite image of Invest 94L, courtesy of RAMMB imagery Colorado State University (CSU).
With little respite from the vertical shear expected, 94L has little chance of developing. Interestingly, the global models portray a more favorable upper air pattern once the system enters the western Atlantic, and on Saturday the system could find itself left behind by the trough currently moving through the upper midwest. Then, amidst a building ridge, the system is forecast to find itself under a diffluent upper flow pattern, which the models -- including the generally reliable GFS and ECMWF -- suggest could allow the system to become a tropical cyclone. Current forecasts for the synoptic scale pattern over the United States at that time indicates a motion toward the northern Florida coast in about five days. It should be noted that the GFS forecasts an environment over the Gulf of Mexico that, although hardly favorable, isn't quite as unfavorable as we've seen in recent weeks, likely due to a temporary northward migration of the subtropical jet. This does not mean I am expecting development. It is questionable whether this system will even survive the next 24 hours. Development is not anticipated while the system is in the Caribbean.
Based on the current center position, 94L is likely to miss south Florida, although in this case, a landfall would pretty much be inconsequential, since all of the associated weather is east of the center in a disorganized band.
Regardless of development, locally heavy rainfall will continue over portions of the Cayman Islands, Cuba, the Bahamas, and south Florida through the next day or so.
Probability of genesis within the next 48 hours: 0%
Bud
Just recently, Bud has become a hurricane, the first of the Eastern Pacific season. As of the latest intermediate advisory from the National Hurricane Center, the following information was posted on the storm:
Wind: 75 mph, with higher gusts
Location: 14.5°N 107.7°W
Movement: N at 6 mph
Pressure: 987 mb
Category: 1 (Saffir-Simpson Hurricane Scale)
Bud is becoming better organized. A ragged eye is now visible in conventional satellite imagery, with a well-defined ring of convection -- no doubt an eyewall, evident in an earlier SSMI overpass. The satellite presentation and inner core have improved since then, and it is possible that the hurricane is undergoing rapid intensification. However, water vapor imagery suggests that southwesterly shear has begun to halt the westward progression of Bud's outflow, but it will take awhile yet to penetrate the inner core region.
Figure 2. Latest infrared satellite image of Hurricane Bud, courtesy of NOAA's Satellite Services Division (SSD).
Bud has about another 18 hours to do what he wants. After that, southerly shear is forecast to increase, waters are forecast to cool, and the cyclone is forecast to ingest a drier airmass. The combination of these factors should lead to weakening, especially beyond 48 hours, when the pace is predicted to become faster. The hurricane should dissipate before the end of the forecast period.
Now for the track. Bud is rounding a weakness along 110W. This should soon turn the hurricane to the north-northeast. Track models are in excellent agreement here. By late Friday and into Saturday, some notable discrepancies arise, with some forecasting the storm to move inland, and others forecasting the center to remain offshore. However, they all agree that the hurricane will come within about 150 miles of the coast regardless, which could lead to a several day period of heavy rainfall and associated flooding.
Because these models are usually reliable when in synchronicity, I will go a forecast track that blends the GFS and ECMWF together. It should be noted that Bud is becoming a large hurricane; tropical storm force winds currently extend out to 115 miles from the center, a significant change from yesterday. It would not be surprising if the wind field grew a little more. This is reflected in the official National Hurricane Center Wind Speed Probability table, which forecasts a 44% chance of tropical storm force winds in Barra Navidad through the weekend, and a 40% chance for Manzanillo. With current arrangements, Bud might not even have to make landfall to produce significant coastal impacts.
5-day intensity forecast
Initial 05/24 0300Z 65 KT 75 MPH
12 hour 05/24 1200Z 75 KT 85 MPH
24 hour 05/25 0000Z 80 KT 90 MPH
36 hour 05/25 1200Z 75 KT 85 MPH
48 hour 05/26 0000Z 65 KT 75 MPH
72 hour 05/27 0000Z 45 KT 50 MPH
96 hour 05/28 0000Z 30 KT 35 MPH
120 hour 05/29 0000Z 25 KT 30 MPH...POST-TROPICAL/REMNANT LOW
5-day track forecast
Figure 3. My 5-day forecast track for Bud.
As a bit of trivia, the last (and only) time a May hurricane occurred alongside a previous May storm was in 1956, although record keeping in this area of the world is vastly more sparse than in the Atlantic.
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