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Matthew drenching Central America and Mexico

By: Dr. Jeff Masters, 3:35 PM GMT on September 25, 2010

Tropical Storm Matthew continues to dump heavy rains over Honduras, Belize, Guatemala, and neighboring regions of Mexico today. Puerto Barrios, in northern Guatemala, has received 4.57" of rain in the past 24 hours. With Matthew expected to slow down and dissipate by Sunday, the storm's heavy rains of 6 - 15 inches can be expected to cause severe flooding and dangerous mudslides. The rains are of particular concern for Guatemala, which suffered its rainiest August in its history, followed by the landfall of Tropical Depression 11E during the first week of September, which dumped torrential rains on the country that triggered flooding and mudslides that killed at least 48 Guatemalans.

Figure 1. Visible satellite image from NASA's Terra satellite taken yesterday, showing Tropical Storm Matthew approaching landfall.

Figure 2. Forecast rain amounts for the 5-day period beginning at 2am EDT today (Saturday, September 25) as predicted by this morning's 2am EDT (6Z) run of the GFDL. Very heavy rains in excess of eight inches (yellow colors) are predicted for portions of Central America along Matthew's track. Image credit: Morris Bender, NOAA/GFDL.

Tropical Storm Lisa pulled a bit of a surprise last night, intensifying into a Category 1 hurricane with 80 mph winds in the far Eastern Atlantic. Lisa's longitude of 27.9W at the time made it the 10th strongest hurricane so far east in the Atlantic. Record keeping began in 1851, but it is likely that many hurricanes stronger than Lisa were missed prior to the advent of reliable satellite coverage in 1974. Lisa is even farther east than Category 4 Hurricane Julia, which earlier this month set the record for strongest hurricane ever recorded so far east. Lisa's glory will be short-lived, though, as strong upper level winds out of the west are expected to increase tonight, bringing high wind shear of 20 - 45 knots over the storm. The high shear may be capable of destroying the storm by early next week. It appears unlikely that Lisa will affect any land areas.

Forecast for the rest of the tropics
Most of the models continue to predict that by Wednesday, the remnants of Matthew, and/or a piece of a tropical disturbance over the Eastern Pacific off the coast of Guatemala, will evolve into a huge and very wet low pressure system that will start spinning over Central America and the Western Caribbean. NHC has been referring to this expected storm as a "monsoon low", and these sorts of storms are very dangerous for Central America and the Western Caribbean, even if they do not develop into a tropical storm. In October 2007, a similar monsoon low I dubbed "the sleeping giant" spent a week spinning over the region, dumping very heavy rains over all of Central America and the countries bordering the Western Caribbean. Rains from this system triggered flooding that killed 45 people in Haiti, damaged thousands of homes in Cuba, and caused havoc in Guatemala, El Salvador, Belize, Mexico, Jamaica, the Cayman Islands, and the Bahamas. A similar type of storm is likely to develop on Wednesday and Thursday, and most of Central America and the nations surrounding the Western Caribbean can expect to see dangerous flooding rains develop this week in association with this giant low. Most of the models also predict that this big low will eventually develop into a tropical storm or hurricane that would be drawn northwards over Cuba late in the week, and threaten the Bahamas, Florida, or the U.S. Gulf of Mexico coast. This is an exceptionally difficult system to forecast correctly, and the models have been coming up with some pretty unusual solutions as to what might happen. We'll just have to wait and see what unfolds over the next few days.

I'll have an update Sunday by 2pm.

Jeff Masters


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