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Western Caribbean disturabance 94L bringing heavy rains; Lupit's path uncertain

By: Dr. Jeff Masters, 2:39 PM GMT on October 21, 2009

A broad 1008 mb low pressure area has developed near 10N 84W, inland over Costa Rica. NHC designated this disturbance Invest 94L yesterday, but is no longer issuing model products for the disturbance. This morning's QuikSCAT pass showed a broad circulation around the low, with top winds of about 30 - 35 mph over the extreme Southwestern Caribbean. Obviously, the center will have to move over water in order for significant development to occur, but recent satellite loops show that the low is pulling in an increasing amount of moisture from the Pacific, leading to heavy rains over Costa Rica and western Panama. Wind shear is low, about 5 - 10 knots, and there is deep layer of high moisture over the entire Western Caribbean, which both favor development if the center moves over water. Rainfall estimates from the Navy Research Lab indicate that 94L dumped up to three inches of rain over portions of Panama, Costa Rica, and Nicaragua over the past 24 hours.

Figure 1. Morning satellite image of Invest 94L.

The forecast for 94L
Wind shear is expected to remain in the low to moderate range, 5 - 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. At present, only the GFS model develops 94L, but weeks it very weak. The GFS predicts the storm will take a north then northwesterly track across western Cuba early next week, then into the Gulf Coast of Florida later in the week. However, it is equally likely that 94L will stay bottled up in the Western Caribbean for the foreseeable future. I'll continue to give 94L a medium (30 - 50% chance) of eventually 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 Friday, which is a good forecast. Given 94L's current state of disorganization and location over land, Saturday 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 Thursday or Friday.

Rick misses Baja, hits Mainland Mexico near Mazatlan
Tropical Storm Rick made landfall near 10am EDT in Mainland Mexico just north of Mazatlan. Top winds measured at the Matatlan airport during landfall were 39 mph, gusting to 61 mph. The primary threat from Rick will be heavy rains of up to six inches in the mountains near Mazatlan. Rick's remains should being at most one inch of rain to south-central Texas on Thursday.

Typhoon Lupit weakens and slows; path now uncertain
Typhoon Lupit, now a Category 1 storm with 90 mph winds, continues to have difficulty dealing with a slug of dry air it wrapped into its core two days ago. Microwave imagery showed that the typhoon was missing a portion of its northern eyewall this morning. However, recent Infrared satellite loops show that the eye has warmed and become more distinct, a sign of intensification. Also, the cloud tops of Lupit's eyewall have cooled in recent hours, signaling that they are more vigorous and reaching higher into the atmosphere. Lupit is in an environment favorable for re-intensification, with low wind shear of 5 - 10 knots and warm sea surface temperatures of 28 - 29°C. It would not be a surprise to see Lupit intensify into a major Category 3 typhoon again by Thursday, though the official forecast from the Joint Typhoon Warning Center is less aggressive, calling for a Category 2 storm by tomorrow. Even in its current weakened state, Lupit is a prodigious rain-maker, with rainfall rates exceeding one inch per hour near its core (Figure 2).

The future path of the typhoon is now highly uncertain, as steering currents are weakening and the storm is slowing down. A weakness in the ridge of high pressure steering Lupit west-southwest is developing, and several models (ECMWF, GFS) now predict recurvature of the typhoon before it reaches the Philippines. This optimistic scenario is counterbalanced by the very pessimistic forecasts of the UKMET and NOGAPS models, which take the typhoon inland over the northern portion of Luzon 1 - 2 days from now, and then stall the storm for 2 - 3 days. This would cause a major flooding disaster, as the soils are already saturated and the dams completely full from the 20+ inches of rain dumped by Super Typhoon Parma in early October. If Lupit stalls for several days over Luzon, it would dump another 20+ inches of rain, triggering massive flash flooding and life-threatening mudslides.

Storm chased Jim Edds is in northern Luzon to document Lupit's landfall, and has some interesting photos of the preparations the residents are taking.

Figure 2. Rainfall rates observed by a polar-orbiting microwave satellite at at 10:24 UTC Wednesday 10/21/09. Lupit is expected to dump rains in excess of one inch per hour (red and pink colors) along its path. Up to 12 inches of rain in a 24-hour period are expected from the typhoon. Image credit: Navy Research Lab, Monterey..

I'll have an update Thursday morning.

Jeff Masters


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