An early start to hurricane season?

The Atlantic hurricane season officially begins on Wednesday, June 1, but the Caribbean is already showing signs of the change of seasons. Moisture and heavy thunderstorm activity have increased in the region between Central America and Jamaica in recent days, and rainfall amounts of 1 - 2 inches have been common over the past three days over Cuba, Hispaniola, and much of Central America. The subtropical jet stream has been bringing high wind shear of 30 - 50 knots over the Caribbean the past week, but this shear has fallen to 20 - 40 knots this morning, and is predicted to fall below 20 knots by Thursday. All of the computer models predict that an area of low pressure will form in the region between Jamaica and Honduras by Thursday. This low will have the potential to develop into a tropical depression late this week. There is some dry air over the Western Caribbean near Mexico's Yucatan Peninsula that may retard the process, but a surge of moisture accompanying a tropical wave currently passing through the Lesser Antilles may counteract this, when the wave arrives in the Western Caribbean on Thursday. Water temperatures in the Central Caribbean are about 1°C above average, 29°C, which is plenty warm enough to support development of a tropical storm. Some recent runs of the NOGPAS model have predicted development of a tropical depression by late this week, potentially affecting Jamaica and Eastern Cuba. The other models have not been as gung-ho, but have been showing the potential for a strong tropical disturbance with very heavy rains forming late this week. In any case, residents of Jamaica, Cuba, the Cayman Islands, Haiti, Honduras, and Nicaragua should anticipate the possibility that heavy rains of 2 - 4 inches may affect them Thursday through Saturday this week.


Figure 1. Total precipitable water (a measure of how much rain would fall if we condensed all the water vapor present) for May 31, 2011 at 7am EDT. Plentiful water vapor in the SW Caribbean would create about 2 inches of rain (50 mm, orange colors) if it were all condensed out. Image credit: University of Wisconsin CIMSS.

Receipt did not travel 525 miles from Joplin tornado
The May 22 EF-5 tornado that struck Joplin, Missouri did not set a new record for longest transport of debris by a tornado. According to MSNBC, a couple living in Royal Center, Indiana, in North Central Indiana, 525 miles from Joplin, found a receipt from the Joplin Tire store three days after the tornado hit Joplin. However, a press release from Purdue University clarified that the receipt did not arrive via the tornado, but had been left behind by a relative that had visited Joplin before the tornado. The longest distance recorded for debris from a storm was a cancelled check that traveled 210 miles after the 1915 tornado in Great Bend, Kansas.

The death toll from the May 22, 2011 tornado in Joplin, Missouri is 139, although there is still considerable uncertainty about this number. The Joplin tornado is the 8th deadliest in U.S. history, and the most deadly since the 1947 Woodward, Oklahoma twister that killed 181 people. The tornado season of 2011 now has approximately 520 deaths, which would make it the deadliest tornado season since 1936, according to statistics compiled by NOAA. In the 1936 tornado season 552 people died, mostly because of violent tornadoes that hit Tupelo Mississippi (216 killed), and Gainesville, Georgia (203 killed.)


Figure 2. Satellite image taken at 23:45 UTC (7:45pm EDT) May 22, 2011, showing the line of tornadic thunderstorms that spawned the Joplin tornado. Image credit: NOAA Visualization Laboratory.

Jeff Masters