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Western Caribbean disturbance less organized; Typhoon Lupit may spare Philippines

By: Dr. Jeff Masters, 1:49 PM GMT on October 22, 2009

A broad 1009 mb low pressure area is over the Southwest Caribbean near 12N 83W, off the coast of Nicaragua. This low, in combination with an upper-level trough of low pressure, is generating some disorganized heavy thunderstorm activity over the Western Caribbean and Central America. A second 1008 mb low pressure area is over the Pacific Ocean near the coast of Costa Rica. The two lows appear to be competing with each other, with the result that the organization of the thunderstorm activity over the region is less than yesterday's. Recent satellite loops show little change in the areal coverage or intensity of the thunderstorms this morning. NHC designated this disturbance Invest 94L on Tuesday, but is no longer issuing model products for it. This morning's QuikSCAT pass missed the Western Caribbean, but last night's pass showed no signs of a surface circulation. Wind shear is moderate, about 10 - 20 knots, and there is a deep layer of high moisture over the entire Western Caribbean, so we still need to keep an eye on this disturbance. NHC is giving 94L a low (less than 30% chance) of developing into a tropical depression by Saturday. No models predict development of this system over the next seven days, but I'll continue to give a medium (30 - 50% chance) that a Western Caribbean tropical depression will form sometime in the next ten days.

NHC is also mentioning an area of disturbed weather over the Bahamas, associated with a trough of low pressure in the upper atmosphere. This disturbance is moving slowly westwards towards Florida, and is under very high wind shear of 40 knots. No development is likely due to the high shear.

Figure 1. Morning satellite image of twin surface low pressure systems, on either side of Central America.

Typhoon Lupit may spare the Philippines
Typhoon Lupit continues to struggle with dry air, which has significantly disrupted the typhoon's inner core, leading to a partial collapse of the eyewall. Lupit is now a minimal Category 1 storm with 75 mph winds. Recent microwave imagery shows that the typhoon is missing a large portion of its western eyewall, and this morning's infrared satellite loop shows that the storm's heavy thunderstorm activity is rather disorganized. Even in its current weakened state, Lupit is a dangerous rain-maker, with rainfall rates exceeding twelve inches per day near its core (Figure 2).

While it is too early to be confident of this forecast, it now appears that Lupit will spare the Philippines a direct hit and a punishing deluge of 12+ inches of rain. The typhoon has slowed in reaction to a collapse of the steering currents, and most of the models are now calling for Lupit to stall just offshore, or recurve to the northeast. The very slow motion of the storm means that it will stir up large quantities of cool water from the depths that will then surround the storm, making re-intensification unlikely, and decreasing the amount of rain the storm is able to produce. The typhoon's core of heaviest rain appears likely to remain offshore, though the extreme northern portion of Luzon Island may still receive 6 - 12 inches of rain before the storm finally departs.

Storm chaser Jim Edds is in northern Luzon to document Lupit's impact, and has photos of the preparations the residents are taking.

Figure 2. Forecast rainfall for the 24-hour period ending at 06 UTC Friday 10/23/09. Lupit is expected to dump rains in excess of twelve inches (red colors) near its core. However, this core of heavy rain will remain offshore over at least the next two days. Image credit: NOAA/NESDIS.

I'll have an update Friday morning.

Jeff Masters


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