MTW Discussion

San Antonio has had yet another 100º day to add to our endless tally of the number of times we have surpassed the century mark — 47. The high temperature at the Airport was 103º after a morning low of 79º. This is the 12th time this month that SA has reached 100º. The good news, however, is some rainfall was observed at the airport — 0.04″. Other parts of town received as much as one inch of rain thanks to thunderstorms that formed along residual outflow boundaries from the Texas Panhandle.

Today, more isolated storms are possible over much of the same areas that saw rain yesterday afternoon. Most of the activity will form with peak daytime heating and die out around sunset. Severe weather is generally not expected out of these storms, but heavy rain, gusty winds, and small hail are certainly within the realm of possibilities. High temperatures will struggle to reach triple-digit levels due to slightly more moist grounds and from rain cooled air around the thunderstorms that develop.

The culprit for these storms is a weakness aloft that is allowing disturbances to propagate southward into South-Central Texas combined with rich tropical moisture, and an endless source of surface heating (our hot temperatures!!). By tomorrow, the weakness will fill in, so to speak, reducing the northerly flow aloft — thus cutting us off from the disturbances up north. That means means our rain chances are also cut off after tomorrow.

Looking at longer range models, by the end of the 8-day forecast period models indicate a return to a southeasterly flow from the Gulf of Mexico. This will open the door to any disturbance/tropical wave in the Gulf into South-Central Texas. Therefore, rain chances next weekend will hover around 10-20%.

The Edwards Aquifer is holding relatively steady, but should go up a bit the next couple of days thanks to some rainfall over the recharge zone yesterday. Additional showers and thunderstorms are possible today. The Stage 3 Water Restrictions Trigger at the J-17 Well in Bexar County is 640 feet above mean sea level. San Antonio has avoided the onset of Stage 3 restrictions at least 3 times so far this summer due to last minute rains. We will continue to monitor the latest levels. Stay tuned for further developments.

TROPICAL UPDATE:

Since the tropics are officially active, I will now divide the near daily discussions into two sections to reduce the clutter.

The National Hurricane Center is currently issuing advisories on Tropical Depression Two in the East Atlantic. The 11 PM ADT update, the storm was located at 14.0ºN, 36.3ºW with maximum sustained winds of 35 MPH moving west at 14 MPH. The minimum central pressure was 1006 mb.

Now yesterday, the storm looked rather impressive with intense, organized convection around the center of the storm. At one point, it may have reached Tropical Storm status. However, the National Hurricane Center rightfully postponed an upgrade as the system showed signs of weakening and was surrounded by an unfavorable environment for further development. The biggest issue is the overabundance of dry air in the mid and upper levels due to the residual Saharan dust in the Eastern Atlantic infiltrating the system. Tropical cyclones need a calm, moist environment to thrive — Tropical Depression Two lacks that. Overnight satellite presentations show further weakening in overall convective trends. Therefore, this storm risks becoming an open wave before regenerating later, if at all. Computer models are in general agreement that in time, Tropical Depression Two will reorganize and strengthen into a weak to moderate tropical storm as it progresses westward. If it does so, its name would become Ana.

However, in the meantime, what Tropical Depression Two is doing is mixing out the dry air in the East Atlantic making the general area fairly moist. The large area of dry air is shrinking rapidly and becoming increasingly negligent. This will leave the door open for the series of disturbances in Africa to head into a moist environment favorable for tropical cyclone formation. The limiting factors, however, are lukewarm, but sustainable sea surface temperatures, and several areas of wind shear. Right now, there is a narrow path of relatively low wind shear for these storms to travel unscathed. The synoptic pattern aloft favors storm movement along this path, therefore storm development is possible.

In fact, the tropical wave behind the Tropical Depression number 2 is of greatest interest right now in the Atlantic. Several global models have been consistent in developing this wave into an intense tropical cyclone within a week or so as it progresses westward. Like its predecessor, it too is performing dismal this morning with its convective activity. However, in time, this will more than likely change as it adjusts to an oceanic environment. This system bears close watching through the next 48 to 72 hours.

Elsewhere in the tropical Atlantic, the National Hurricane Center flagged a couple areas near the Lesser Antilles for possible development. Right now there is a disturbance producing several storms over the islands. A couple models hint that it might organize into a tropical cyclone and move into the Gulf of Mexico. At this time, there is a low probability of intense organization, but as always we’ll keep an eye on it.