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Little change to 96L; El Salvador flood among its worst in history

By: Dr. Jeff Masters, 2:55 PM GMT on October 22, 2011

A region of disturbed weather in the Western Caribbean (Invest 96L) is bringing heavy rains to coastal Nicaragua and Honduras, and has the potential to develop into a tropical depression Sunday or Monday. Visible satellite loops show that 96L has changed little in organization since yesterday. Some rotation is apparent, but the heavy thunderstorm activity is quite limited due to a large region of dry air to the east, as seen on water vapor satellite loops. There are no signs of a surface circulation. Surface pressures have been falling since Thursday at San Andres Island, near the center of 96L. Wind shear is a moderate 10 - 20 knots in the region, and is expected remain in the moderate range through Tuesday. Water temperatures are very warm, 29 - 30°C, and these warm waters extend to great depth.

Figure 1. Morning satellite image of 96L.

Forecast for 96L
The moderate wind shear and warm waters should allow for some development of 96L over the next few days, though this will be slowed by the dry air to the storm's east, and perhaps by proximity to the land areas of Nicaragua and Honduras. The models are less enthusiastic today about developing 96L into a tropical depression than they were yesterday. The ECMWF no longer predicts development, and the GFS and NOGAPS predict only weak development before 96L moves ashore over Honduras on Tuesday. On Wednesday, a strong trough of low pressure will be passing over the Eastern U.S., and this trough has the potential to turn 96L northwards into Western Cuba. This is more likely to happen if 96L is stronger and deeper, and thus able to "feel" the upper-level winds the trough will bring. The UKMET model predicts 96L will develop into a tropical storm that moves through the Yucatan Channel between Cuba and Mexico on Thursday. If 96L remains a weak and shallow system, though, it is more likely to stay trapped in the Western Caribbean and make landfall in Nicaragua or Honduras. NHC gave 96L a 60% chance of developing into a tropical depression by Monday in their 8 am Tropical Weather Outlook today. The hurricane hunter mission scheduled for today was cancelled due to the lack of development of 96L; the mission has been re-scheduled for Sunday afternoon.

A broad region of low pressure near 10°N, 57°W, about 400 hundred miles east of Trinidad (Invest 97L), is moving slowly west-northwest towards the Lesser Antilles Islands. This low has very limited heavy thunderstorm activity, due to dry air to the northwest. NHC is giving 97L just a 10% chance of developing into a tropical depression by Monday. 97L is under a moderate 10 - 20 knots of wind shear, and this shear is expected to drop to the low range, less than 10 knots, by Monday, when the storm will be in the Eastern Caribbean Sea. By the time 97L approaches Jamaica in the Central Caribbean in 5 - 6 days, the storm should find a moister environment, and there is a chance for 97L to develop into a tropical depression, as predicted by the NOGAPS model.

Figure 2. Rainfall in El Salvador for the 10-day period ending on Friday, October 21, at 8 am EDT. At Huizucar, an astonishing 1.513 meters (4.96 feet) of rain fell during those ten days. Image credit: Hydrological Service of El Salvador.

Death toll from Central American rains rises to 105
“I want to tell the world that El Salvador is going through one of the most dramatic disasters in its history,” President Mauricio Funes said on national radio and television Wednesday night, as he appealed for international aid. A week of torrential rains across Central America have triggered extreme floods and landslides that have killed 105 people, according to media reports. El Salvador, Guatemala, Honduras and Nicaragua have declared states of emergency due to the disaster. El Salvador and Guatemala have seen the worst flooding, with 34 and 38 people killed, respectively. Another 18 have died in Honduras, 13 in Nicaragua, and 5 in Costa Rica. The rains were due to a large area of low pressure that was moistened by the landfall of Tropical Depression 12-E near the Mexico/Guatemala border last week. Contributing to the record-intensity rains were ocean temperatures off the coast of El Salvador that were 0.5 - 1°C above average during the first half of October, allowing more water vapor than usual to evaporate into the air. Over the past ten days, rainfall amounts of over a meter (39.4") have fallen over a large area of southwest El Salvador (Figure 2.) At Huizucar, an astonishing 1.513 meters (4.96 feet) of rain fell in the past ten days.

I'll have a new post on Sunday.

Jeff Masters

Flood Hurricane

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