Saturday, March 26, 2005

On South Padre Climates

I sat down to write about the weather, but let me start with a note about folks who like to brandish stuff after their names, like Dr., Jr., III ("Trey"), JD, MPA, MD, and so forth. My dad has a PHD but folks don't call him "doctor." I have a Master of Geography but please don't call me "MAG" and I don't ever use the moniker.

But all geographers love climatology and the weather. Some folks think that grographers won a key WWII battle by surprising the Nazis during the Normandy Invasion (D-Day). Surfers, now those are budding little geographers because they can predict waves, sometimes much better precision than the big-government weather folks, the NOAA. Suffice it to say that the weather in Austin and South Padre is completely different.

That's because the two towns are in completely different climactic zones. Austin's climate is more influenced by continental air masses, while South Padre is predominantly a coastal marine area. What's the difference?

Let's look at the summertime, when fewer cold fronts sweep the state. A continental high pressure cell will form over New Mexico and wander almost overhead in Austin. This means dry and hot, with clockwise winds spinning most of the wind from the southeast. Down at the coast, the same winds flow but they have something call the "sea-breeze effect" that can set up some major showers, and perhaps even a few water spouts (funnel clouds over the Gulf). These showers don't happen all the time and it is very difficult to predict them.

The Laguna Madre makes things even more interesting, as it is an unusually warm body of shallow water. Interaction with sea breeze and the Laguna micro-region and the Rio Valley can lead to some interesting little thundershowers.

I hate to be on the beach during a thunderstorm, given the lightning stike potential (more people are hit by lightning in Florida than bit by any shark, alligator, all animals combined). So one day I watched this black cloud come up from Mexico ... and said "Honey, let's boogie back to the barn." So we scampered home in the midst of a few of those really fat raindrops. And then ... nothing.

So considering myself an amateur expert, I was completely miffed. I sat on the porch and watched that black cloud turn up to Brownsville, nail Harlingen (2 inches of rain), and then circle back over the north end of the island, making a big giant circle back to where it began. I beleived that storm was mocking me!

After seeing that about five times, over the years, I began thinking (thought you smelled wood smoke, eh?). So I did some research and contacted some weather gurus such as Troy Kimmel and Mark Murray up here in Austin. The answers, while complex and confusing, seemed to help.

What happens sometimes is a coastal trough develops about 20-40 miles off Padre beaches, roughtly running parallel to the beach. Sometimes you can see the cloud bank off the beaches. The sea breeze develops about 10:00 in the morning and leaves the trough to travel northwest (sometimes the sea breeze gets all the way to Austin, providing some much needed farmer's rain). If there is any instability over the region, larger than expected thunderstorms can develop. That can create "outflow boundaries" that have cooler air at the edges. Sometimes these outflow boundaries can develop even larger storms, which tend (we're guessing here) to push from the north back to the south. A special kind of double-low pressure system known as a tropical upper trough (TUTT Low) can also produce similar results.

All this doesn't sound very satisfactory but it will have to do for now. The weather dudes were careful to say that the average thunderhead only lasted about 15-30 minutes, so what I was watching was a series of cells that appeared to move as one in a circular pattern (he did ask if I had a beer or two, also! That's an Aggie for ya.). I hope we get to see lots of these little black clouds because South Padre Island is normally a very, very dry place, maybe 20 inches of rain a year as compared to almost twice that much up in Austin.

This just in: Dr. Gray has just released his preliminary 2005 hurricane season outlook, and it's not a good one. Eleven named storms, a number he says could be revised upwards. He mainly blames it on unusually warm ocean currents. We'll be watching those coastal troughs and TUTT systems in the early part of the seaon, since those are the ones that would be most likely to impact the lower Texas coast. I'll have more to write on those, as the season progresses, but "retrograde" lows that curve to the west are the most dangerous for us.

As a final note, three major hurricanes hit the Bahamas and Florida last year, and the only way to get through to my folks was on satelite phones and satelite Internet. The only way for them to transmit was with a satelite dish - that hadn't blown away - and a generator for the juice and repowering the phone batteries. So, when I get the bucks, you know what I'll be buying! Best regards,

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