U.S. heat wave blamed for 22 deaths; Bret and Cindy no threat

The dangerous U.S. heat wave of July 2011 will continue to bring another day of exceptionally humid heat to over 100 million Americans today, with 33 states plus the District of Columbia currently under heat advisories. The heat index--how hot the air feels when factoring in both the temperature and the humidity--exceeded 100° in twenty states in the Central and Eastern U.S. on Wednesday, peaking at 123° in Council Bluffs, Iowa. At least 22 deaths are being blamed on the heat in the Midwest. The extreme humidity that has accompanied this heat has made it a very dangerous one, since the body is much less able to cool itself when the humidity is high. The high humidities are due, in great part, to the record rains and flooding in the Midwest over the past few months that have saturated soils and left farmlands flooded. Accompanying the heat has been high levels of air pollution, which also contributes to mortality. Air pollution is expected exceed federal standards and reach code orange, "Unhealthy for Sensitive Groups", in at least 22 states today, according to the latest forecasts from EPA.

The extreme heat peaked in Chicago yesterday, where the temperature hit 100° at Midway Airport and the Chicago Lakefront station. Rockford, Illinois hit 100°, the first time in 22 years that city had seen 100° temperatures. Detroit is expected to hit 100° for the first time in sixteen years today, and I think I'm going to skip the Ann Arbor Art Fair! New York City and the mid-Atlantic states are expected to be near 100° on Friday. The forecast high of 103° in Washington D.C. for Friday is just 3° below the hottest temperature ever recorded in the city, 106°. The heat will continue in the mid-Atlantic states through Sunday, then ease on Monday when a cold front is expected to pass through. Wunderground's climate change blogger Dr. Ricky Rood has some good insights on the current heat wave in his latest post. A few notable highlights from this week:

Omaha, Nebraska has been above 80° for a four-day period beginning on July 17. This is the 2nd longest such stretch on record, next to the 8-day period that ended July 25, 1934. Multi-day periods when the low temperatures do not cool off below 75° are associated with high heat wave death rates.

Amarillo, Texas recorded its 26th day of 100° temperatures yesterday, tying the city's record for most 100° days in a year, last set in 1953. Record keeping in the city goes back to 1892.

Minneapolis, Minnesota, recorded its highest dew point ever, 82°, on Tuesday. The heat index hit a remarkable 118° in the city, which tied July 11, 1966 for the highest heat index on record in the city. Minnesota's all-time highest dew point temperature of 86° was tied on Sunday, in Madison. The previous record was in St. James and Pipestone in July of 2005.

The latest National Weather Service storm summary has a list of cities where the heat index exceeded 100° yesterday.


Figure 1. On Wednesday, heat advisories for this dangerous heat wave covered portions of 33 states plus the District of Columbia, an area with 141 million people--about half the population of the U.S.

Tropical Storm Bret no threat
Tropical Storm Bret continues to struggle with high wind shear of 20 - 30 knots, and high shear is expected to affect the storm the remainder of the week. The combination of high wind shear and dry air nearby should act to destroy Bret by Sunday, and the storm is not a threat to any land areas.

Tropical Storm Cindy forms
Tropical Storm Cindy formed yesterday 600 miles to the east of Bermuda. Cindy's formation was 24 days ahead of the usual formation date for the third named storm of the Atlantic hurricane season, which is August 13. This year has the most early season activity since 2008, when Hurricane Dolly got named on July 20. Wind shear is a moderate 10 - 20 knots, and is expected to remain moderate for several days. However, Cindy has moved over cool ocean waters of 25°C this morning, and this temperature is 1.5°C below the threshold of 26.5°C that tropical storms typically need in order to maintain their strength. With Cindy predicted to move over waters of just 21°C by Friday morning, the storm doesn't have long to live. Cindy is not a threat to any land areas.

An African wave worth watching
An African wave near 12N 50W, 700 miles east of the Lesser Antilles Islands, is moving west to west-northwest at about 15 mph, and is generating a limited amount of heavy thunderstorms due to the presence of a large amount of dust and dry air from the Sahara. This wave will spread heavy rain showers and strong gusty winds to the northern Lesser Antilles beginning on Saturday. The wave has a modest degree of spin to it, and is under low wind shear, 5 - 10 knots. Once it finds a moister environment near the Bahama Islands early next week, it could develop. Of the latest 00Z and 06Z runs of the four reliable models for predicting formation of a tropical depression, only the NOGAPS model shows development of the wave. The NOGAPS predicts the wave could attain tropical depression status on Wednesday, just off the coast of South Carolina. The other models generally depict too much wind shear over the Bahamas for the wave to develop. The eventual track of the wave once it reaches the Bahamas early next week is uncertain; there will be a trough of low pressure located off the U.S. East Coast that will be capable of turning the wave to the north, along the East Coast. However, it is also quite possible that the wave would be too weak and to far south to feel the influence of this trough, and instead would enter the Gulf of Mexico.


Figure 2. Morning satellite image of Hurricane Dora.

Hurricane Dora in the Eastern Pacific close to Category 5
Hurricane Dora in the Eastern Pacific put on an impressive burst of intensification over the past 24 hours, and is now a very impressive Category 4 storm with 155 mph winds, just 1 mph short of Category 5 status. Dora is expected to move parallel to the coast of Mexico, and should not cause any major trouble in that country. Dora is the second major hurricane in the East Pacific this year; Hurricane Adrian topped out as a Category 4 storm with 140 mph winds in early June.

Think cold. Way cold!
Those of us sweltering in today's heat would do well to consider that on this date in 1983, Vostok, Antarctica shivered at -128°F--the coldest temperature ever measured on Earth. The low tonight in Vostok is expected to be a relatively balmy -80°F.

Jeff Masters