Western Caribbean disturbance 94L organizing; Rick wanes; Lupit still dangerous

A broad 1010 mb low pressure area has developed near 13N 81W in the Western Caribbean, about 300 miles east of the Nicaraguan coast. NHC designated this disturbance Invest 94L this morning. This morning's QuikSCAT pass showed no evidence of a surface circulation, and not even much of a shift in wind direction associated with the low. Wind shear is moderate, about 10 - 20 knots, and there is deep layer of high moisture over the entire Western Caribbean, which will aid development. The heavy thunderstorm activity associated with 94L has not increased in intensity or areal coverage much over the past 24 hours, but it has begun getting more organized, with some curved bands beginning to form, indicating that a circulation at middle levels of the atmosphere may be starting to spin up. The disturbance will bring 3-day rain totals of 4 - 8 inches to eastern Nicaragua and northeastern Honduras through Thursday, as 94L moves slowly northwestward. As the storm organizes, it may begin to pull moisture from the Pacific across Costa Rica, Panama, and Nicaragua, resulting in flooding rains of 4 - 8 inches along the Pacific slopes of those countries Wednesday through Friday.


Figure 1. Current satellite image of Invest 94L.

The forecast for 94L
The SHIPS model forecasts that wind shear will remain in the moderate range, 10 - 15 knots, for the next five days in the Western Caribbean. Sea Surface temperatures are very warm, 29°C, and there is plenty of moisture through a deep layer of the atmosphere. The only major impediment to 94L becoming a tropical storm later this week would seem to be proximity to land. Most of the models foresee a path taking 94L very close to the coast of Nicaragua and then along the north coast of Honduras, and the storm may move inland over one of these countries before it has time to develop into a tropical depression. Due to proximity to land, I give 94L just a medium (30 - 50% chance) of becoming a tropical depression over the next ten days. NHC is giving 94L a low (less than 30% chance) of developing into a tropical depression by Thursday, which is a good forecast. Given 94L's current state of disorganization, Friday is the earliest we should expect it to organize into a tropical depression. NHC has not put the Hurricane Hunters on call to fly 94L Wednesday or Thursday. The ECMWF model foresees that 94L will move northwards next week across Cuba and threaten South Florida, but none of the other models are predicting this. It is too early to know if 94L will be a threat to more than just Central America.

Rick wanes
Tropical Storm Rick has faded from its glory as the second strongest Eastern Pacific hurricane of all time to a mere tropical storm, thank to continued moderate to high wind shear of 15 - 25 knots over the past 36 hours. The shear has managed to inject dry air that lies to the west of Rick directly into its core, which significantly disrupted the storm. With the shear expected to continue at 15 - 25 knots between now and landfall in mainland Mexico on Wednesday afternoon, it is unlikely that the storm will be able to take advantage of the warmer sea surface temperatures it will find along its path over the next 24 hours and re-intensify. It looks like the southern tip of Baja will miss the more severe right-front quadrant of the storm, and NHC is currently giving both Cabo San Lucas and San Jose Cabo on Baja's southern tip just a 50% chance of receiving tropical-storm force winds of 39 mph or greater. The main threat from Rick will be heavy rains over the mountains of Mexico when Rick penetrates inland on Wednesday evening. South Texas can expect just 1 - 2 inches of rain from Rick's remains on Thursday and Friday.

Typhoon Lupit weakens, but still dangerous for the Philippines
Typhoon Lupit has weakened to a Category 2 storm with 95 mph winds, thanks to some dry air that wrapped into the typhoon's core over the past 24 hours, which disrupted the eyewall. It appears from satellite and microwave imagery that Lupit's eyewall is attempting to re-form now, as no more dry air is being sucked into the storm. Lupit is headed west towards a landfall Thursday on the northern portion of Luzon Island in the Philippines. 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 will increase sharply in the final 12 hours before landfall, and it would not be a surprise to see Lupit re-intensify into a major Category 3 storm before landfall.

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. 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 2. Rainfall forecast for Typhoon Lupit for the 24-hour period ending at 06 UTC Wednesday 10/21/09. Lupit is expected to dump rains in excess of 12 inches (red colors) in a small region near its center. Image credit: NOAA/NESDIS.

Cool video
NOAA's Environmental Visualization Laboratory has put together a 4-minute Flash video of the 2008 hurricane season. Infrared satellite imagery for each hour of each day during the 6-month season is looped, and it is fascinating to watch the daily build-up of thunderstorms progress from east to west across the country as each day waxes and wanes. Note that as we head into September this thunderstorm activity diminishes as the continent cools.

I'll have an update Wednesday morning.

Jeff Masters