TD 5 strugging; 121° in Oklahoma; little change to U.S. drought

A disheveled Tropical Depression Five is clinging to life in the face of stiff wind shear and dry air, as the storm heads towards the Lesser Antilles Islands with a forward speed of 20 mph. The depression is very ragged looking on visible satellite loops. The depression has only a small area of heavy thunderstorms, which are on the south side of the center due to high wind shear and dry air on the northern side of the storm. Wind shear over TD 5 is at the moderate level, 15 - 20 knots. Water vapor satellite loops show that TD 5 is at the southern edge of a large area of dry air. Wind shear due to strong upper level winds from the west is driving this dry air into the core of the storm, disrupting it. The first Air Force hurricane hunter aircraft will investigate TD 5 Thursday afternoon to give us a better idea of its strength.


Figure 1. Morning satellite image of TD 5.

Forecast for TD 5
TD 5's west to west-northwest motion should bring its outer rain bands to Barbados early Friday morning, and high winds and heavy rain will spread over the rest of the Windward Islands by Friday afternoon. Since wind shear will be higher on the storm's north side, I expect the heaviest weather will be on the south side of TD 5, over the Windward Islands. Wind shear is expected to remain moderate, 10 - 20 knots, through Friday, according to the 8 am EDT run of the SHIPS model. However, the reliable ECMWF model predicts higher shear on Friday and Saturday, which could tear TD 5 apart. A number of our reliable computer models predict TD 5 will not survive its passage through the islands this weekend. However, most of the models agree that once TD 5 (or its remnants) pass enter the Central Caribbean on Monday, wind shear will fall to the low range, and strengthening (or regeneration) can occur. Once TD 5 enters the Western Caribbean between Jamaica and Mexico's Yucatan Peninsula, a trough of low pressure passing to the storm's north may be capable of turning TD 5 more to the northwest, resulting in the storm entering the Gulf of Mexico. An equally likely scenario at this point is that TD 5 will not turn, and instead will take a more westerly path over the Yucatan Peninsula. The long-term forecast for what the storm will do once it gets to the Western Caribbean depends upon whether or not TD 5 survives during the next two days.


Figure 2. High temperatures yesterday in Oklahoma from the Oklahoma Mesonet.

Extreme heat in Oklahoma
Wednesday was the hottest day in Oklahoma since August 1936, said wunderground's weather historian, Christopher C. Burt, with more than half of the state recording temperatures of 110° or higher. The hot spot Wednesday: 121° in Freedom, in the northwest part of the state. If verified, this temperature would beat Oklahoma's all-time state temperature record of 120°, set in Tipton on June 27, 1994, and at three locations in 1936. The official temperature at the Oklahoma City airport hit 112° Wednesday, tied for the city's 2nd highest temperature since record keeping began in 1890. The only hotter day was August 11, 1936, when the temperature hit 113°. Other hot spots in Oklahoma yesterday:

118° at station W1DY (just north of Oklahoma City's Wiley Post Airport)
116° at Claremore
115° at Chandler, Enid, Guthrie, Okmulgee, Omega, and Kingfisher

Thursday's forecast calls for a high temperatures of 113° in Oklahoma City, which would be the hottest temperature in the city's history. You can see the extreme high of 121° in Freedom, OK using the NWS Mesonet Observations tool.

It was also brutally hot in northern Texas, with the hottest temperature a 118° reading at station DW3597 in Wichita Falls, Texas. This is just shy of the state record of 120° set on August 12, 1936, in Seymour. The Wichita Falls airport hit 112°, which was just 1° below the all-time hottest August temperature ever measured in the city (113° on August 8, 1964.)

Little change to the U.S. drought during the past week
The great U.S. drought of 2012 remained about the same size and intensity over the past week, said NOAA in their weekly U.S. Drought Monitor report issued Thursday, August 2. The area of the contiguous U.S. covered by drought dropped slightly, from 64% to 63% over the past week, and the area covered by severe or greater drought stayed constant at 46%. If we average the past five drought monitor reports to come up with unofficial July drought numbers for the contiguous U.S., the 2012 drought is second only to the great Dust Bowl drought of July 1934 in terms of the area of the contiguous U.S. covered by moderate or greater drought:

1) Jul 1934, 80%
2) Jul 2012, 62%
3) Dec 1939, 60%
4) Jul 1954, 60%
5) Dec 1956, 58%

If we consider the area of the contiguous U.S. covered by severe or greater drought, my unofficial calculations show that 2012 ranks in 5th place:

1) Jul 1934, 63%
2) Sep 1954, 50%
3) Dec 1956, 43%
4) Aug 1936, 43%
5) Jul 2012, 41%

The U.S. Department of Agriculture has now declared more than half of all counties in the U.S. (50.3%) natural disaster areas due to the drought, adding 218 counties in 12 states to its disaster list on Wednesday. In all, nearly 1,600 counties in 32 states have been declared disaster areas.


Figure 3. July 31, 2012 drought conditions showed historic levels of drought across the U.S., with 64% of the contiguous U.S. experiencing moderate or greater drought, and 46% of the county experiencing severe or greater drought. Image credit: U.S. Drought Monitor.


Figure 4. The twice-monthly U.S. Drought Outlook, updated on Thursday, August 2, predicts that drought will continue through October over most of the U.S., Some expansion to the north and south is expected, but also some improvement over the Eastern U.S. and Southwest U.S. Image credit: NOAA Climate Prediction Center.

Drought predicted to extend into October
In their twice-monthly drought outlook, released on Thursday August 2, NOAA's Climate Prediction Center had this to say about the Midwest drought: Unfortunately, the self-perpetuation of regional drought conditions, with very dry soils and very limited evapotranspiration, tends to inhibit widespread development of or weaken existing thunderstorm complexes. It would require a dramatic shift in the weather pattern to provide significant relief to this drought, and most tools and models do not forecast this. Unfortunately, all indicators (short and medium-term, August, and August-October) favor above normal temperatures. With much of the Plains already in drought and getting worse, above normal temperatures expected into the fall, and a dry short-term and 30-day forecast, the drought should persist, with some possible development in the northern Plains.

One bright spot: drought conditions are expected to improve over the Southwest U.S. over the next few weeks, as the annual summer monsoon peaks and brings heavy rains. The Southeast U.S. has seen some improvement over the past week. The potential for a landfalling tropical storm to bring drought-busting rains during the August - September - October peak of hurricane season led NOAA to predict possible improvement in drought conditions over the Southeast U.S.

Drought already creating global ripples
The U.S. is the world's largest exporter of corn and wheat, and 3rd largest exporter of soybeans. According to the Christian Science Monitor, food price increases due to the U.S. drought is already causing unrest in other parts of the world: "Take Indonesia, where soybeans are used to make tofu, the staple protein for the country's poor. There, soybean prices have risen 33 percent in the past month, and are already causing tensions. On July 26, there were clashes in Jakarta and other major cities in markets as a coalition of tofu producers sought to enforce a national production strike protesting against a 5 percent soybean import duty."

Jeff Masters