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 , 7:30 PM GMT on September 02, 2009
Tropical Storm Erika remains weak and disorganized, and the future track and intensity of the storm remain highly uncertain. The center has jumped several times over the past 12 hours, and now lies exposed to view, west of the main area of heavy thunderstorms. Radar animations out of Martinique show little organization of the echoes, and satellite imagery shows no low-level spiral bands or upper-level outflow. Wind shear analyses from the University of Wisconsin diagnose a moderate 10 - 15 knots of shear over Erika, a decrease from yesterday. SSTs are warm, 29°C. The Hurricane Hunters are in the storm now, and have found a slight increase in the surface winds, up to 45 mph. They noted that the surface center was displaced 12 miles north of the center they found at 1500 feet, which is the sign of a disorganized storm undergoing wind shear.
The forecast for Erika
Erika is embedded in a weak steering current pattern, and the storm's current state of disorganization is allowing the center to make random jumps as it reforms near the heaviest thunderstorm activity. This makes for a low-confidence forecast. The future track of the storm will depend upon how strong the storm gets over the next few days. A stronger Erika will extend higher into the atmosphere and be steered more to the northwest by upper-level winds. A weaker Erika will be steered more by the low-level winds, which will keep the storm on a more westerly track. The intensity forecast models did a poor job with Tropical Storm Danny last week, and appear to be repeating that poor performance with Erika. All of the major intensity forecast models predict substantial strengthening of Erika. This seems unlikely to occur, given the storm's current disorganization, and the predicted increase in wind shear along the path of Erika to 20 - 25 knots 3 - 5 days from now. The more southerly than expected track of the storm also brings the possibility that Erika will encounter the high mountains of Puerto Rico and Hispaniola. The GFS, GFDL, and Canadian models predict Erika will pass near Puerto Rico on Friday, then move over Hispaniola on Saturday. Erika in its current weak state would probably not survive an encounter with these islands. A wide range of scenarios is still possible for Erika, from outright dissipation (as forecast by the GFS, Canadian, and ECMWF models) to intensification to a Category 3 hurricane (as forecast by the HWRF model). Erika is a long-term threat to the Bahamas and U.S. East Coast if it is still around five days from now. Potential landfall locations range from Florida on Tuesday to North Carolina on Wednesday. The NOGAPS model has Erika potentially missing the U.S. entirely, scooting northwards between North Carolina and Bermuda. My current expectation is that Erika will dissipate on Saturday when it encounters Hispaniola.
Figure 1. Afternoon image of Tropical Storm Erika. The swirl of clouds just west of Guadeloupe island is the center. This center was what I had labeled a "false center" in this morning's post, and has taken over as the main center this afternoon.
Hurricane Jimena hits Baja
Hurricane Jimena made lanndfall on Mexico's Baja Peninsula late this morning near Cabo San Lazaro as a Category 2 hurricane with 100 mph winds. Jimena is the 2nd strongest hurricane to hit Baja's west coast since record keeping began in 1949. The only stronger storm was Hurricane Norbert, which made landfall in 2008 on the central Baja coast with sustained winds of 105 mph. Jimena has now weakened to a Category 1 storm, and will continue to weaken as it hits colder waters and interacts with land. No deaths or major damage have been reported from the storm.
Figure 2. Hurricane Jimena on Tuesday, Sep. 1, 2009, as seen by NASA's MODIS instrument. Image credit: NASA Earth Observatory.
California fire webcams
As I discussed in yesterday morning's post, you can use our wundermap for Los Angeles with the fire layer turned on to see where the fire and smoke are located, and track the temperatures and winds during today's air pollution event. We also have two webcams with views of the fire: Altadena and Tujunga.
I'll have an update Thursday morning.
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