Parkersburg tornado an EF-5; major flooding in Central America likely from 90E

The tornado that devastated Parkersburg, Iowa on Sunday has now been rated an EF-5 by the National Weather Service. An EF-5 is the strongest possible classification a tornado can receive, and is only given to those tornadoes with estimated winds over 200 mph. The winds in the Parkersburg tornado were estimated at 205 mph. At those wind speeds, total destruction of homes occurs. Even those sheltering in basements are not safe--several of the six deaths from the Parkersburg tornado were from people sheltering in basements.

The Parkersburg tornado cut a path 43 miles long and between 3/4 miles and 1.2 miles wide across Iowa, killing six people, completely destroying 350 buildings in Parkersburg, and injuring 70 people. It was only the second EF-5 tornado this decade in the U.S. The other EF-5 occurred in May 2007, when much of Greensburg, Kansas got leveled. The Parkersburg tornado was the first F5 or EF5 tornado in Iowa since the Jordan, Iowa tornado of June 13, 1976, and was the second deadliest in Iowa since official record-keeping began in 1950. Iowa's deadliest tornado hit Charles City on May 15, 1968, killing 13 while producing F5 damage.


Figure 1. EF-5 damage from the May 25, 2008 Parkersburg tornado. At EF-5 winds speeds (over 200mph), homes are completely destroyed or removed from their foundations. Image credit: Iowa Helicopter. The NWS Des Moines office has posted ground damage photos from their damage survey.

Major flooding likely in Central America from 90E
An area of low pressure (90E) in the Eastern Pacific off the coast of Costa Rica, near 10N 88W, is steadily organizing and appears likely to develop into a tropical depression later today or tomorrow. The National Hurricane Center is currently assigning a "High" probability (>50% chance) that this will be a tropical depression, in its new experimental Tropical Weather Outlook. Satellite loops show that the low has developed a very large and expanding circulation. This circulation is likely to expand across Central America into the Western Caribbean, allowing the storm to tap moisture from the Atlantic and Pacific. Storms that are able to tap the moisture sources of both oceans can be extremely dangerous rainmakers, even if they are weak tropical depressions. Already, 90E is generating very heavy rains in excess of six inches per day near its center. The storm is expected to move northeastward over Costa Rica or Nicaragua by Thursday or Friday, and should being dangerous flooding rains of 5-10 inches to those nations and Panama. Most of the computer model guidance suggests that the storm will then track to the north, spreading very heavy rains across Guatemala, El Salvador, Honduras, Belize, and southern Mexico by Saturday. These heavy rains will cause life-threatening flash flooding, particularly in mountainous regions.

Since 90E is beginning to dominate the circulation pattern of the region, it appears unlikely that a tropical depression will form in the Western Caribbean in the coming week, as some computer models have been predicting. It is possible that 90E could cross Central America and pop out in the Western Caribbean near the Yucatan Peninsula, or in the Gulf of Mexico's Bay of Campeche. However, the crossing of Central America will severely disrupt the storm, and the odds of 90E becoming a depression in the Atlantic basin are low.


Figure 2. Observed precipitation for the 24 hours ending at 12Z (8am EDT) Wednesday May 28, 2008. Rainfall amounts in excess of 2000mm (eight inches, yellow colors) occurred near the center of disturbance 90E off the Pacific coast of Costa Rica. Image credit: U.S. Navy Monterey.

I'll have an update Thursday morning.

Jeff Masters