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. marraskuuta 2009 klo 15:21 (GMT)
Hurricane Ida is threading the gap between Cuba and Mexico's Yucatan Peninsula as a Category 1 hurricane, and now appears poised to bring a punishing combination of high tides and heavy rain Monday night and Tuesday morning to the U.S. Gulf Coast. Ida is a compact hurricane, and radar imagery out of Cancun (Figure 1) reveals a tight inner core, with only limited rain bands affecting Mexico and western Cuba as the storm shoots through the Yucatan Channel. Top winds at Cancun, Mexico this morning have only been 15 mph, despite the fact that Ida is passing just 60 miles east of the city. Infrared and visible satellite loops show little change to Ida's heavy thunderstorm over the past six hours, and the hurricane appears to have changed little since the last Hurricane Hunter aircraft left at 6:30 am. A new Hurricane Hunter mission is scheduled for 1 pm EST this afternoon.
Wind shear has increased over the storm since yesterday, and is now a high 20 - 25 knots. However, the storm is over some of the warmest waters in the Atlantic, with SSTs at 29°C, and the total ocean heat content a very high 100 kJ/cm^2.
Figure 1. Radar image of Ida from 9:28 am EST 11/08/09 from the Cancun, Mexico radar. Image credit; CONAGUA.
The forecast for Ida
The high wind shear of 20 - 25 knots currently affecting Ida is forecast to persist at that level until Monday night. Some slow intensification is still possible while Ida remains over the exceptionally warm water of the Loop Current in the Gulf of Mexico, through tonight (Figure 2). Late tonight, Ida will be crossing over waters of 26°C, which is barely enough to support a hurricane. With shear still expected to be at 20 -25 knots, I expect weakening to begin early Monday morning and accelerate on Monday afternoon. At that time, Ida will encounter 40 knots of wind shear associated with a cold front over the Gulf of Mexico, and begin transitioning to an extratropical storm. Exactly how strong Ida will be when it reaches the coast early Tuesday morning--and indeed if Ida even does reach the coast--is a forecast with high uncertainty. The computer models have a tough time forecasting the evolution of a tropical cyclone into an extratropical cyclone, and the models are all over the place on what will happen. Most of the models foresee a landfall near 1 am EST Tuesday between Mississippi and Pensacola, Florida, then a path northeastward over the Southeast U.S. However, Ida could come to halt before reaching the coast and turn east towards Tampa (the UKMET model's forecast), or turn south back over the Gulf of Mexico (the NOGAPS model's forecast). In any case, storm surge and heavy rain appear to be the main hazards from Ida. The GFDL model (Figure 3) is forecasting rain amounts of 4 - 8 inches for a large swath of the Gulf Coast, and there is a risk of tornadoes if the warm air from the core of Ida pushes ashore.
Figure 2. SSTs in the Gulf of Mexico, with the forecast track of Ida from Sunday's 10 am EST NHC forecast superimposed. Image credit: NOAA/AOML.
Storm surge is the other concern. With a strong high pressure system anchored voer the U.S. today, the pressure difference between this high and Ida is creating a strong pressure gradient that will drive tides 3 - 5 feet above normal from New Orleans to the Florida Panhandle tonight. As Ida approaches on Monday, an additional rise in water of another two feet is possible, and a large stretch of coast will be subject to very high water levels for an extended period of time. With high winds of 45 - 55 mph likely to build Monday afternoon into Tuesday morning, significant coastal erosion event is shaping up. A particular concern is the low-lying, heavily developed western end of Alabama's Dauphin Island, where storm surges from four hurricanes over the past fifteen years have caused heavy damage.
Figure 3. Total rainfall amounts from the 1 am EST Sunday 11/08/09 run of the GFDL model. Image credit: Morris Bender, NOAA/GFDL.
I'll have an update later today.
Links to follow:
U.S. Severe Weather Page
Comments will take a few seconds to appear.