Tropical weather analysis - September 24, 2010
Lisa
Hurricane Lisa unexpectedly went through a period of rapid intensification today, which brought it from a minimal tropical storm to a minimal hurricane in just about 8 hours. Here is the latest information on Lisa as of the 11:00 PM AST advisory from the National Hurricane Center:
Wind: 80 mph, with higher gusts
Movement: N at 8 mph
Pressure: 987 mb
Location: 20.7°N 27.9°W
Category: 1 (Saffir-Simpson Hurricane Scale)
Infrared satellite loops depict a very small but well-organized hurricane, though the small eye observed earlier has since filled in.
Figure 1. Latest infrared satellite image of Hurricane Lisa.
A recent SSMI/S microwave satellite overpass indicates that Lisa still has a small but well-defined eye and eyewall, despite the former not being readily apparent on conventional satellite images.
Upper-level winds are still currently pretty favorable, but water vapor imagery and CIMSS data indicate that strong vertical shear lies just to the north of the hurricane. Given that, Lisa only has a very narrow window of opportunity with which to undergo any additional intensification, perhaps less than 12 hours.
In fact, the 18z GFS implies that vertical shear will begin to increase across the system in as little as twelve hours, as Lisa loses her anticyclone. Vertical shear is expected to remain prohibitive throughout pretty much the entire forecast period, and thus no significant strengthening is anticipated. Indeed, given Lisa's small size, she may weaken even quicker than is currently being indicated by the NHC:
INITIAL 25/0300Z 20.7N 27.9W 70 KT
12HR VT 25/1200Z 21.9N 28.1W 75 KT
24HR VT 26/0000Z 23.7N 28.3W 65 KT
36HR VT 26/1200Z 25.0N 28.5W 55 KT
48HR VT 27/0000Z 26.4N 28.8W 45 KT
72HR VT 28/0000Z 28.5N 29.2W 30 KT
96HR VT 29/0000Z 30.5N 29.5W 25 KT...POST-TROP/REMNT LOW
120HR VT 30/0000Z...DISSIPATED
As of now, I agree pretty well with this intensity forecast from the NHC, and will allow for the possibility of some slight additional strengthening throughout the overnight hours.
Lisa will also have dry air to deal with over the next several days.
Lisa appears to have turned very slightly to the left over the last couple hours based on satellite imagery, though the overall movement is still N.
Water vapor imagery depicts a mid- to upper-level trough and associated cutoff low digging southward to near 35W.
Lisa should continue moving generally N throughout the entire forecast period as the aforementioned trough gradually lifts out to the east. This will not allow for the subtropical ridge to build in much. Based on all the steering data I've analyzed, I concur pretty strongly with the NHC's current forecast track:
Figure 2. Latest NHC 5-day forecast track for Lisa.
I know it seems like often times I regurgitate the NHC's information, but that's because I usually find very little reason to disagree with them. In the rare instances I actually feel justified in having a disagreement(s) with them, I'll gladly lay it out.
Matthew
Tropical Storm Matthew continues moving inland over northern Honduras, running roughly parallel to the Caribbean Sea. Here is the latest information on the system as put out by the National Hurricane Center at 11:00 PM EDT:
Wind: 50 mph, with higher gusts
Pressure: 998 mb
Movement: WNW at 15 mph
Location: 15.2°N 85.0°W
Category: Tropical storm
Infrared satellite loops, reconnaissance data, and surface observations indicate that Matthew has maintained strength despite being overland for several hours at this point. Over the last hour or so, Matthew has been generating cloud tops in excess of -80C or greater over a rather large area. This convection is very likely only temporary, however, likely being enhanced by orographic lift along the Honduran mountains.
Figure 3. Latest infrared satellite image of Tropical Storm Matthew.
As Matthew continues inland tonight and encounters the high mountains of Honduras, this convection should weaken, and as a consequence, so should the surface winds. However, Matthew should remain close enough to the Caribbean Sea as to maintain tropical storm status throughout Saturday. In addition, even though Matthew's winds will gradually slacken, the threat for torrential rainfall across Nicaragua, Honduras, Belize, Guatemala, and the Yucatan Peninsula is certainly quite likely over the next several days. These rains will likely cause life-threatening flash flooding and mudslides.
Indeed, I suspect that localized amounts as high as 25 inches could occur across the mountainous portions of these areas over the next few days, particularly Honduras.
Both the GFDL and HWRF show Matthew landfalling in Belize as a tropical storm on Saturday evening, with the former showing a 55 kt storm. I will not rule out the possibility of some slight restrengthening of Matthew once it briefly emerges over the Gulf of Honduras, but it will have very limited time to do so and I will not be surprised if it doesn't.
I suspect that Matthew will be over the Gulf of Honduras in about 12 hours, based upon current and forecast forward speed, as well model data.
Matthew will probably only spend about 6-12 hours over the Gulf of Honduras, and I tend to go with the lower estimate, but will compromise and keep it over water for 8 hours.
Matthew should be destroyed over the mountains of wstern Guatemala or eastern Mexico in about two days, possibly less.
Despite this however, I want to once again emphasize that Matthew poses the threat for torrential, flooding rains and associated mudslides across Central America and Mexico over the next several days, and unfortunately, there will likely be loss of life, possibly significant.
Watches and warnings
A TROPICAL STORM WARNING IS IN EFFECT FOR...
* THE COAST OF HONDURAS...INCLUDING THE OFFSHORE ISLANDS
* THE COAST OF BELIZE FROM BELIZE CITY SOUTHWARD
A TROPICAL STORM WATCH IS IN EFFECT FOR...
* THE COAST OF BELIZE NORTH OF BELIZE CITY
Elsewhere
Elsewhere in the tropics, the global models are once again unanimously predicting the formation of another tropical depression in the western Caribbean Sea in about five days. This system does not appear to be related to Matthew, but rather, is a separate entity. Given the large amount of moisture currently draped across the Caribbean, the formation of this system cannot be ruled out.
The models suggest that it will pose a threat to Jamaica, western Cuba, south Florida, and the Bahamas, and interests in these areas should closely monitor the progress of this potential system over the next several days.
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