Hot, Rain Free Weather to Continue for most of Deep South Texas through July 19 (click to enlarge)
Hot and Mainly Rain Free Until Further Notice
Drought, Wild Fire Danger Continues

Like a broken record, the searing heat continues in Deep South Texas. While the region is known for its hot and humid summers, the persistence of the heat, relatively gusty southeast winds, and lack of any widespread rain events for most areas since early June has been impressive. For July, average temperatures through the 13th were 3.1°F above average at Brownsville, 3.7°F above average at Harlingen, and a whopping 6.3°F above average at McAllen. For McAllen's Miller Airport, all but two days surpassed 100°F, with an average high of nearly 104°F! As of this writing, no end was in sight to the heat and largely rain free weather. The continuing dry, breezy, and hot conditions will maintain moderate to exceptional drought across the region and keep a critical threat for rapid wild fire growth. On July 6th, the combination of gusty winds, low humidity, and critically dry ground fuels allowed a fire to grow rapidly to more than 250 acres on ranchland north of Miller Road near Federal Highway 281, near San Manuel in Hidalgo County.

Why? Maybe, Blame it on "NAO"!
While El Niño has returned, it has not been a factor in the Deep South Texas heat spell. Other oceanic – atmospheric patterns, referred to as teleconnections, might be in play. The North Atlantic Oscillation (NAO) is one such pattern. This pattern is perhaps the most prominent of all teleconnections, occurring in all seasons and sometimes "assisting" the development of other teleconnections. As with all patterns, there exist positive and negative phases of the NAO. While summer correlations between the NAO and surface temperature are less clear, in general, the positive phase generally leads to slightly below average temperatures across Texas in July; the reverse is true for the negative phase. Since early June, the NAO has been in a prolonged negative phase (below).

North Atlantic Oscillation, state from May through mid July, 2009 (click to enlarge)

How long will this phase continue? Global model ensembles suggest at least another week or longer (below). This means virtually no change to the current conditions as we head toward late July. The resulting atmospheric pattern near 18 thousand feet tells the tale, featuring a dominant, sprawling high pressure ridge stretching from the southwest U.S. through the western Gulf of Mexico, including all of Deep South Texas, and a persistent trough or zonal (west to east) flow from the Midwestern U.S. through the mid–Atlantic and Northeast. The image at right shows the 500 mb pattern as of 7 AM CDT Sunday, July 12th (above, right). Until the ridge and trough shift substantially, noticeably cloudier and wetter conditions will not affect the Valley.

North Atlantic Oscillation, ensemble forecast through late July, 2009 (click to enlarge)

The combination of heat and humidity will make it feel more like 102°F to 107°F each afternoon across most of the area. Evenings will provide little relief as the apparent temperature will remain above 90 until after midnight for areas away from the coast. The potential for heat health related incidents continues, even during this hottest part of the year. Persons expected to spend any length of time outdoors for the next week are urged to follow safety tips, at right:

Typical 500 mb pattern for June into July 2009 (click to enlarge)
  • Slow Down. Schedule strenuous activities early in the morning, if at all.
  • Drink Plenty of Water. For healthy persons, be sure to drink water at all times, even if you are not thirsty. Persons on fluid restricting diets should consult their physicians before increasing consumption.
  • Dress for Summer. Lightweight, light colored clothing reflects heat and sunlight and helps maintain a lower body temperature.
  • Do not Drink Alcohol. Alcoholic beverages increase dehydration rate and could bring on heat stress or heat stroke rapidly.
  • Spend time in Air Conditioning. Cooler locations offer relief and some protection from heat dangers.
  • Avoid Sunburns. Sunburn makes heat dissipation from the body more difficult. As the summer solstice approaches, the angle of the sun reaches its peak, increasing the threat for sunburn in a short period of time.
  • Eat Lighter. Put less fuel on your inner fires. Foods that increase metabolic heat production can also increase the rate of water loss.
  • Never Leave Children Unattended in Vehicles. Not even for a minute! Temperatures rise rapidly inside a car, nearly 30°F in as little as 20 minutes. Click here for more information on children and hyperthermia.
For much more information, go to the National Weather Service's Heat Safety web page.


Drought Stress
According to the Texas A&M Agrilife Extension Service, the current drought continues to affect the production of grains and native rangeland and pastureland. Across the area, the grain harvest is expected to be small; supplemental feeding continues for cattle and other livestock. Windmills and water wells continued to be used as a main source of water for livestock. Heavy irrigation of corn, sorghum, and citrus was allowing these crops to progress.

Wildfire Growth Potential
Dry to Critically Dry Fuels will continue across all of Deep South Texas, as widespread, soaking rains are not in the forecast. Moderate afternoon winds gusting in excess of 25 mph combined with marginally low humidity will keep at least an elevated threat for rapid wild fire growth. Burn bans remain in effect for most counties in Deep South Texas and all of the Rio Grande Valley. Parking vehicles or using grinding or other sparking machinery in grassland is highly discouraged. Residents with further questions about any burning should contact local officials.

Beating the Heat: The Beach
The prolonged heat and abundant sunshine has been a boon to beach goers and the Town of South Padre Island. July 2009 is shaping up to the the opposite of July 2008, which began with clouds and rain from upper level disturbances and finished with Dolly’s heavy winds and rain. Healthy crowds each day are great for business, but also provide more opportunity for those entering the surf to experience rip currents and longshore swell. The general weather pattern looks to remain benign, with east to southeast winds continuing at 10 to 15 knots and a light to moderate swell which should remain below 7 seconds. Experienced swimmers should find the pleasantly cooler waters a great way to beat the heat. Inexperienced swimmers should remain cautious, particularly where rip currents tend to form near the jetties of Isla Blanca Park, and at remote beach access points where deeper water can make navigating undertow associated with longshore swell more difficult.

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