At last!  Thunderstorms and tapering rains reach a large portion of the Lower Rio Grande Valley
Clouds, rain, and green(er) grasses are seen at the NWS Office in Brownsville, August 30th.

It's Finally Over
Thunderstorms Break Heat Wave, but Records will Fall

Relief Continuing into Early September

Update, August 30 Rain in the Valley: Foretelling?
Believe it! At long last, everything came together for scattered to numerous drenching thunderstorms across the Lower Rio Grande Valley, from Port Isabel to Rancho Viejo, Harlingen, and Weslaco. As of 5 PM on August 30th, 3.01 inches had fallen in Rancho Viejo, between 1 and 3 inches had fallen in and near Harlingen, and nearly 1 and 1/2 inches fell in Bayview, all in a three hour period on Auugst 30th. These rains complete the coverage for all of Deep South Texas since late on August 28th, when a complex of thunderstorms formed across the Rio Grande Plains of Webb County during the evening. Energy driving east and southeast from the initial cluster soon developed a complex which rolled into northeast Zapata, central and northern Jim Hogg, and much central and northern Brooks County. Torrential rains dropped between 1 and 3 inches across these areas (above). More storms developed on the evening of the 29th as fresh boundaries and an upper level disturbance act on unstable air and reached into Starr, portions of Hidalgo, and southern Zapata County. Stay tuned for a full update on August 31st. Until then, the searing heat continues in the Valley, but will soon modify.

Heat Starting to Wane
While the blistering heat will finally come to a close, several all time monthly records and even a few all time summer (June through August) records are about to break, eclipsing the swelter that was 1998. 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 remains impressive. Temperature data collected for June through August 26th, compared with other similar periods, show most stations in Deep South Texas and the Rio Grande Valley in the top 5 hottest, all time. As of August 26th, McAllen Miller Airport was 1.1°F above its all time average, while Harlingen was in second place. Brownsville, with the longest period of record – more than 130 years – has risen to 5th. 1998 remains the benchmark summer for many in Deep South Texas; however, June and July’s were the matching hot months, while in 2009 July and August have closely matched values.

August temperatures look to break all time records in several locations, ensuring that 2009 will challenge 1998 for heat supremacy in Deep South Texas. Table 1 below shows the 2009 summer averages, historical rank, and standing record; Table 2 shows the same for August, 2009. Thus far, through August 26th, temperatures were running 2.5°F above average at Brownsville (86.7°F), 2.6 degrees above Harlingen (87.4°F) and 5.7°F above average at McAllen/Miller (92.0°F).

McAllen Miller Airport: Wow!
As of August 29th, 2009, some interesting facts from McAllen/Miller Airport:

  • 41 new or tied high temperature records in 2009 thus far.
  • 49 straight 100°F days. On August 30th, Miller airport fell two degrees shy, courtesy of approaching thunderstorm winds. This blows away any previous records. In 1998, there were several stretches of 15 or more days at or above 100°F, broken by one or two days below.
  • 69 100°F days from June 1st through August 27th, 18 more than every year except 1998, when there were 71 (73 if missing June data are assumed to be 100°F based on previous and next day’s values.
  • Average summer high temperature, so far, in 2009: 102.0°F!

 

Table 1: Average Temperatures, June 1st through Aug. 26th (preliminary data)
Station
2009 Average
Rank
All-Time Record
Year
McAllen/Miller Arpt. (since 1961)
91.0
1
89.9
1998
McAllen/Coop (since 1941)
89.2²
1
88.6
1998
Port Mansfield (since 1958¹)
85.2
1
85.0
2005
Port Isabel (since 1928¹)
85.9
2
86.0
1998
Harlingen/Coop (since 1911)
86.9
2
88.0
1998
Rio Grande City (since 1900¹)
89.7
2
91.6
1998
Falcon Dam (since 1962)
89.4
2
91.4
1998
Raymondville (since 1913¹)
86.9
5
88.4
1998
Brownsville (since 1871)
85.9
5
87.1
1998

¹Data incomplete, especially early in 20th century.
²Summer 2009 missing 20 or more dates (incomplete)

Table 1: Average Temperatures, August, 2009 (through 26th, preliminary data)
Station
2009 Average
Rank
All-Time Record
Year
McAllen/Miller Arpt. (since 1961)
92.0
1
89.3
1998
McAllen/Coop (since 1941)
90.1²
1
89.1
1997
Brownsville (since 1871)
86.7
T-1
86.7
2005
Port Mansfield (since 1958¹)
86.1
1
85.9
2005
Port Isabel (since 1928¹)
86.7²
2
87.7
1928
Harlingen/Coop (since 1911)
88.0
2
88.9
1958
Raymondville (since 1913¹)
87.8
T-3
88.2
1920
Falcon Dam (since 1962)
90.2
4
91.1
1997
Rio Grande City (since 1900¹)
90.5²
5
92.9
2001

¹Data incomplete, especially early in 20th century.
²August 2009 missing 6 or more dates (incomplete)

Pattern Beginning to Change...
Very dry air deep into the atmosphere became anchored across all of South Texas by August 25th, courtesy of high pressure settled into the southern third the U.S., extending into the northern tropics west of 85°W longitude. By the end of the week and into the weekend (28th through 30th), a deepening trough of atmospheric low pressure will begin spreading south and east across the eastern half of the nation. Unlike events earlier this summer, this trough will gradually strengthen a cold front which will make a move into portion of the Deep South, extending to the Southern Plains, as the month ends. This system will actually squeeze the atmospheric high pressure, and associated hot, dry conditions, through Deep South Texas, ensuring that through at least the 29th and perhaps to the end of the month, more of the same with more triple digit heat ahead.

September: Early Changes Ahead?
While the full effects of the front will not reach into south Texas, the lifting associated with its presence may...just...provide...relief! Such lifting, enhanced by upper level disturbances moving underneath the base of the trough, would greatly increase atmospheric moisture in a band that would spread across northeast Mexico and Deep South Texas as August ends and September begins. Increased moisture, combined with some atmospheric cooling, could finally bring much welcome rain for some, if not all, of the Rio Grande Valley, and solidly break the streak of excessive heat (below). After the clouds and any rain departs, temperatures may well return to average, with high temperatures between 90 and 95. Stay tuned to this website for forecast updates as September arrives.

Rains, lower temperatures may arrive in the Lower Rio Grande Valley and Deep South Texas to begin September
Possible weather pattern across the U.S. to start September, 2009 (click to enlarge)

Until the End of August
The combination of heat and humidity, particularly near the coast, will make it feel more like 102°F to 108°F each afternoon across most of the area. Evenings will provide little relief as the apparent temperature will remain between 85 and 90 until after midnight for areas away from the coast. The potential for heat health related incidents continues. Now that autumn scholastic athletic training is underway and schools have opened across the Rio Grande Valley, persons expected to spend any length of time outdoors are urged to continue following safety tips, below:


  • 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 Agilife Extension Service, the drought has begun taking a direct toll on cattle herds in Deep South Texas. A recent report notes that dryland crops such as cotton and corn are nearing total losses in the Rio Grande Valley, but irrigable crops, fed by water storage at dam reservoirs on the Rio Grande River, are actually doing quite well. Dryland crop damage has exceeded $10 million, and is expected to reach $25 million or more when assessments are completed this autumn. For more on the drought as it stands in late August, check out the August 21st "Droughtlook".

Local wild life is also feeling the effects of the heat and drought. At the Laguna Atascosa National Wildlife Refuge in northeast Cameron County, native animals are having to trek to a cistern system, scattered across the park, to drink water, which lacks a steady supply of irrigation water. Even in parks with enhanced water supplies, the lack of general moisture has reduced the ability of many plants to flower, which in turn reduces the numbers of butterfly species.

Wildfire Growth Potential
Dry to Extremely Dry Fuels will continue across all of Deep South Texas through the end of August, as drought and heat continue. Fortunately, surface to 20 foot winds have quieted a bit, which should help reduce the rate of speed of any wild fire. Still, afternoon winds 10 mph combined with marginally low humidity will keep at least an elevated threat for rapid wild fire growth on most days through August 30th. 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. More super weather will continue through the weekend for "The Island". 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 6 seconds. Most swimmers should find the pleasantly cooler waters a great way to beat the heat; the rip current risk is expected to remain low through the end of August.

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