Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.
By: Dr. Jeff Masters , 8:01 PM GMT on July 22, 2010
Tropical Depression Three is steadily organizing, and appears poised to become a much stronger storm than was forecast. Water vapor satellite loops show that the upper level low to the west of TD 3 that has been bringing high levels of wind shear to the storm is now moving faster to the west than predicted. This faster motion has resulted in a reduction in wind shear over TD 3, to a moderate 10 knots. Satellite images of TD 3 show that the storm is taking advantage of the lower shear by developing several low-level spiral bands to the north and east of the center. However, the center of circulation is still exposed to view, and dry air is still getting injected into the core of the storm from the southwest. The storm's heavy thunderstorms have not increased in intensity this afternoon, and the amount of heavy thunderstorm activity near the core of the storm is still limited. TD 3 will need to build more intense thunderstorms near its center before significant intensification can occur. TD 3 is a small storm, and surface observations in the Bahamas do not show the circulation very well. An outer rain band of TD 3 is now visible on Miami long-range radar, and a flood watch has been issued for all of South Florida. The Hurricane Hunters are in the storm at present, and have found top surface winds of 35 - 40 mph.
Figure 1. Afternoon satellite image of TD 3.
Track Forecast for TD 3
The storm is in a straightforward steering current environment, and TD 3 should progress steadily to the west-northwest through Sunday. This will bring the storm ashore over the Florida Keys or South Florida on Friday, and into the Gulf of Mexico on Saturday. The latest set of model runs from 8am EDT (12Z) foresee a track more to the north than the previous set of model runs. This increases the threat to the oil spill region, and I give a 40% chance that the oil spill region will see tropical storm force winds of 39 mph or higher this weekend. Oil recovery and relief well drilling operations should cease. If TD 3 makes a direct hit on the oil spill region as a tropical storm with 50 - 60 mph winds, it will likely drive a storm surge of 3 - 6 feet with high waves on top into the Louisiana marshlands, fouling a large area with oil. Oil would also penetrate into Lake Pontchartrain, which lies just two feet above sea level. However, the wave action of the storm will dilute the oil to some degree, which may limit the damage to the marshlands.
If you are wondering about the specific probabilities of receiving tropical storm force winds at your location, I recommend the wind probability product from NHC. The latest 5 pm probabilities of various locations getting tropical storm force winds, 39 mph or higher:
Marco Island 43%
New Orleans 33%
Intensity Forecast for TD 3
The primary detriment to development of TD 3 for the next three days will be the presence of the large upper-level low to its west. If the low remains in its present location, relative to TD 3, it will bring wind shear of about 10 knots to the storm. This will allow for steady intensification of perhaps 20 mph per day, and TD 3 could be a hurricane by Sunday at that pace. However, if the upper-level low slows down a bit, relative to TD 3, more shear and dry air will affect the storm, potentially weakening it. None of the computer models is calling for TD 3 to strengthen into a hurricane, but if the shear continues at 10 knots, I expect TD 3 will become a hurricane. My low-confidence intensity forecast gives TD 3 a 40% chance of becoming a hurricane. NHC is putting the odds of TD 3 being a hurricane at 2 pm Sunday at 15% with their 5pm advisory.
An area of disturbed weather (98L) has developed in the Gulf of Mexico's Bay of Campeche. This system is under a low amount of shear, 5 - 10 knots, and probably does not have enough time to organize into a tropical depression before making landfall along the Mexican coast a few hundred miles south of the Texas border on Friday.
Resources for the BP oil disaster
Map of oil spill location from the NOAA Satellite Services Division
My post, What a hurricane would do the Deepwater Horizon oil spill
My post on the Southwest Florida "Forbidden Zone" where surface oil will rarely go
My post on what oil might do to a hurricane
NOAA's interactive mapping tool to overlay wind and ocean current forecasts, oil locations, etc.
Gulf Oil Blog from the UGA Department of Marine Sciences
Oil Spill Academic Task Force
University of South Florida Ocean Circulation Group oil spill forecasts
ROFFS Deepwater Horizon page
Synthetic Aperture Radar (SAR) imagery from the University of Miami
I'll have an update in the morning. ABC World News Tonight will probably show a sound bite I did for them today, on their 6:30pm broadcast.
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