The month of September 2010 was warmer and drier than normal. For most of the month, the Sub-Tropical upper air high pressure ridge was in control. The ridge began weakening late in the month, lowering temperatures gradually until the pattern change to Autumn came on the 25th. This brought near to below normal temperatures for late in the month. Compared with September 2009, the month was 4.2 deg. Warmer, and 5.80 in. Drier.
Year-to-date rainfall through month's end was 3.68 in. Less in 2010 than in 2009. The thirty-day outlook had called for near normal temperatures and above normal precipitation.
The week August 29-September 4 saw near normal temperatures and rainfall about 125 percent of normal. During the first part of the week, a weak upper air trough generated afternoon showers, and held temperatures to near normal levels. A cold front crossed on the 2nd, returning showers and lowering daytime highs and drying out the atmosphere by the 4th. The week's average temperature was 80.1 deg., and rainfall was 0.84 inch. This was 3.8 deg. Cooler than the previous week. Compared with the same week in 2009, the week was 4.0 deg. Warmer, and there was no rainfall in 2009.
The week September 5-12 saw near normal temperatures and rainfall about 125 percent of Normal. Tropical Storm Hermine made landfall in North Mexico south of Brownsville on the night of the 6th, and moved slowly northward through Central Texas until exiting the state on the night of the 8th. Spiral bands rotating around Hermine brought the area's rain, and lowered temperatures at mid- week. Early and late in the week, upper air high pressure was in control, and temperatures were several degrees above normal. The week's average temperature was 80.0 deg., which was 0.1 deg. Cooler than the previous week. Rainfall was 0.90 inch. The week was 0.5 deg. Warmer and 0.23 inch wetter than the same week in 2009.
The week September 12-18 saw temperatures about 5 deg. above normal, and no measurable rainfall. Upper air high pressure controlled the region's weather during the week. Early and late in the week, the air mass was moist, leading to warm overnight lows. At mid-week, the air mass dried out somewhat, with minimum temperatures in the high 60s. The week's average temperature was 82.9 deg., which was 2.9 deg. Warmer than the previous week. A trace of rain fell on the afternoon of the 17th. Compared with the same week in 2009, the week was 8.8 deg. Warmer, and 5.27 inches drier.
The week September 19-25 continued the trend of very warm and dry weather, with temperatures running about 5 degrees above normal, and no rainfall. There was slight weakening in the Sub-Tropical upper air high pressure ridge early in the week, permitting slight cooling until compressional heating of the strong cold front which crossed on the 26th took over a couple of days earlier. The week's average temperature was 81.3 deg., 1.6 deg. Cooler than the previous week. Compared with the same week in 2009, the week was 10.8 deg. Warmer, and 0.91 inch drier.
The final five days were dry. The period began cool, with the season's first heating degree- days coming on the 27th. Temperatures warmed through the 30th as the modified Polar air mass modified.
The reporting period for temperatures and phenomenon on each day is for the twenty-four hours ending at midnight hours GMT--6 p.m. CST and 7 p.m. CDT. The reporting period for precipitation is for the twenty-four hours ending at noon GMT--6 a.m. CST and 7 a.m. CDT. All times are given using the twenty-four hour clock, and are expressed in Greenwich Mean Time.
Observations are from NWS Station 41/9207/4 in Tyler, Texas. The term "normal" refers to averages from the standard climatic period 1971-2000.
MX MN OBS PCPN REMARKS
September 2010, RECORDS AND SUMMARY: