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Rick weakens; Lupit headed to the Philippines; Western Caribbean brewing a storm?

By: Dr. Jeff Masters, 2:09 PM GMT on October 19, 2009

Hurricane Rick has weakened significantly over the past 24 hours, thanks to moderate wind shear of 15 - 20 knots. Although still a powerful Category 3 hurricane with 125 mph winds, this is a far cry from the spectacular Category 5 hurricane with 180 mph winds and 905 mb pressure Rick was early Sunday morning. At that time, Rick was the second most powerful hurricane ever recorded in the Eastern Pacific. The only Eastern Pacific hurricane that was stronger was Hurricane Linda of 1997, which had 185 mph winds and a 902 mb pressure. Reliable satellite measurements of Eastern Pacific storms go back to about 1970, and Rick is the 11th Category 5 hurricane in the Eastern Pacific since 1970.

Figure 1.Hurricane Rick just after peak intensity at 17:55 UTC October 18, 2009. A this time, Rick was a Category 5 hurricane with 175 mph winds. Image credit: NASA.

Recent microwave satellite imagery suggests that wind shear may have eaten away the southwest portion of Rick's eyewall, allowing dry air to intrude into the core of the storm. The Hurricane Hunters will visit Rick this afternoon to learn more, and I suspect Rick is weaker than the Category 3 hurricane with 125 mph winds that is currently advertised.

Wind shear will increase to the high range, 20 - 30 knots, in the 24 hours before landfall, and ocean heat content and sea surface temperatures will steadily decrease over the next two days as Rick approaches Baja. The latest GFDL and HWRF model runs put Rick at Category 1 strength at its closest approach to Baja, and this appears to be a reasonable forecast given the current appearance of Rick. NHC is currently giving both Cabo San Lucas and San Jose Cabo on Baja's southern tip a 20% chance of receiving hurricane-force winds from Rick. Rick will make a second landfall in Mainland Mexico on Wednesday night, and the moisture from Rick should reach southern Texas by Friday, possibly leading to heavy rains there on Friday and Saturday.

Typhoon Lupit a potential major disaster for the Philippines
Category 4 Super Typhoon Lupit has begun its turn to the west over the Philippine Sea, and is headed towards a landfall early Thursday morning on the northern portion of Luzon Island in the Philippines. Thanks to the departure of a trough of low pressure that was pulling the super typhoon to the northeast and creating a region of weak steering currents, a strong ridge of high pressure is now building in over Lupit and will force it slightly south of due west. The models are all in excellent agreement on the forecast track taking the super typhoon over northern Luzon as a major Category 3 or 4 typhoon, and Lupit--the Filipino word for cruel--is very likely to live up to its name. The northern Philippines are still reeling from the rains and mudslides unleashed by Super Typhoon Parma last week, which crossed over the northern Philippines three times, dumping over twenty inches of rain in many locations. Parma killed 438 people, and 51 are still missing. A week prior to Parma, Typhoon Ketsana brought the heaviest rains in 42 years to the capital of Manila, killing 420 people, with 37 still missing.

Figure 2. Rainfall forecast for Super Typhoon Lupit for the 24-hour period ending at 06 UTC Tuesday 10/20/09. Lupit is expected to dump 8 - 12 inches of rain (orange colors) in a small region near its center. Image credit: NOAA/NESDIS.

Wind shear over Lupit is in the low range, 5 - 10 knots, and the typhoon is embedded in a very moist environment with warm sea surface temperatures of 28 - 29°C. Total heat content of the ocean is too low (20 kJ/cm^2) to permit much additional intensification over the next two days, but in the final 12 hours before landfall, the total oceanic heat content will rise to 80 kJ/cm^2, which should allow Lupit to retain at least Category 3 strength right up until landfall, despite interaction of the storm with land. Lupit will move relatively quickly over the Philippines, but the typhoon is likely to dump 12+ inches of rain over the already saturated soils of northern Luzon Island. These rains will create life-threatening flash floods and mudslides capable of killing hundreds more Filipinos.

Figure 3 Morning visible satellite image of the area of disturbed weather in the Western Caribbean.

A Western Caribbean tropical storm coming?
In the Atlantic, an area of disturbed weather has developed in the Western Caribbean from Costa Rica to the Cayman Islands, in association with the remains of a cold front, a tropical wave, and a broad 1010 mb low pressure region that has developed over the extreme southwestern Caribbean off the coast of Costa Rica. Last night's QuikSCAT pass showed that the low off the coast of Costa Rica had a broad and disorganized surface circulation. The thunderstorm activity associated with this large and complicated area of disturbed weather is disorganized and under 10 - 30 knots of wind shear, and any development over the next three days will be slow. However, by Friday, wind shear over the Western Caribbean is expected to drop significantly, and development of a tropical depression in the Western Caribbean becomes a more real possibility. Numerous runs over the past few days of all of our reliable global forecast models have shown a tropical depression developing in the Western Caribbean by early next week. The timing, location, and track of such a such a storm are all pretty hazy, but I think there is a 60% chance of a named storm forming in the Western Caribbean sometime in the next 10 days. The regions most likely to be affected by such a storm would be Honduras, Nicaragua, and the Cayman Islands, and it is possible that such a storm may stay trapped in the Western Caribbean for many days (as predicted by the GFS model). Alternatively, the storm could move steadily northwards after formation, affecting western Cuba, the Cayman Islands, Jamaica, South Florida, and the Bahamas. This is the solution preferred by the ECMWF model. In either case, a long period of disturbed weather is likely for the Western Caribbean. Heavy rains will affect northeast Honduras, eastern Nicaragua, and the Cayman Islands this week, and could spread to adjacent countries as the area of disturbed weather evolves.

Jeff Masters


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