August, Summer 2009 records end up in dust bin in portions of the Lower Rio Grande Valley

August, in Review
While Deep South Texas and the Rio Grande Valley are known for their hot and humid summers, 2009 was unique. The persistence of the heat, relatively gusty southeast winds, and lack of any widespread rain events until the month’s dying days brought average temperatures once again to the brink of prior records in most areas, with records shattered once again across the most populated locations in the Valley, from Weslaco to McAllen. The arrival of clouds and welcome rains on the final two days of the month may have saved coastal locations from new records; nonetheless, nearly every observing station had monthly average temperatures land in the top 5, all time.

Table 1 shows 2009 average August temperatures, rankings, and standing or broken records for locations where sufficient data were available. Similar to July, both McAllen/Miller Airport and the nearby cooperative observing station at the water treatment plant shattered their prior records set in 1998. Miller airport was just under 2.1°F (2.04°F) above its 1998 benchmark, and the water treatment plant was a healthy 1.3°F ahead of the mark. Weslaco had the next record, and a healthy difference (0.7°F) above its prior record. To put these departures in perspective, note once again that the value of 2.1°F is roughly one standard deviation about the August mean temperatures. See box below for more unique information from McAllen Miller this summer. A discussion of the August statistical relationship, which nearly mirrors that in July, can be found in the July 2009 Review. Final August departures from average are shown in the map above. For the three airport locations, temperatures were 2.2°F above average at Brownsville (86.2°F), 2.3 degrees above Harlingen/Valley (86.8°F) and 5.3°F above average at McAllen/Miller (91.4°F).

Summer 2009’s Searing Heat
What a difference a year makes! While June, 2008, was relatively hot and dry and comparable to June, 2009 with less wind, July and August were mirror opposites, with July 2008’s early tropical moisture and drought denting rains finished off with the torrents of Dolly. The soaking rains helped mitigate the typically hot mid summer temperatures, as solar energy was spent on evaporation as well surface heating. By late August, more deep tropical moisture invaded Deep South Texas, this time favoring the Rio Grande Plains with incredible downpours in Starr and Zapata County.

Summer (June through August) 2009 was a case where both atmospheric and earth science puzzle pieces fit together to create a feedback loop: Favorable atmospheric patterns maintained the hot, windy, and rain free weather, and the excessive heat at the earth’s surface was reinforced by the parched landscape, allowing the sun’s energy to be used exclusively for heating, which in turn increased surface winds between the relatively cool Gulf and the hot land more than even a relatively hot atmospheric pattern would allow. The winds accelerated the pace of drying, leading to more heating, as the cycle continued through the heart of summer. By the end of August, a break in the pattern would allow moisture to pool along the Rio Grande into northern Mexico; showers and thunderstorms, lighter winds, increased humidity, and longer nights would finally tame the heat wave.

This pattern of endless heat ensured that 2009 would challenge 1998 for heat supremacy in Deep South Texas. Temperature data collected for June through August showed most stations in Deep South Texas and the Rio Grande Valley in the top 5 hottest, all time. McAllen Miller Airport was nearly 1°F above its all time average, while Harlingen’s cooperative station was in second place. Brownsville, with the longest period of record – more than 130 years – ended in 6th. Table 2 below shows the 2009 summer averages, historical rank, and standing record.

The Legacy
1998 remains the benchmark summer for most in Deep South Texas, but 2009’s persistent heat through July and August, added to shorter heat waves in early May and early June, will not soon be forgotten. The hot, dry weather finished off most dry land crops such as corn and cotton; if not for the stores of water from the 2008 torrents, irrigated crops such as citrus and other fruits might have suffered a similar fate. There is hope that the developing El Niño will bring hope to drought stricken communities in all of South Texas.

Some interesting facts from McAllen/Miller Airport as Summer 2009 Closes: