Wetter Than Normal Summer/Fall 2012 For RGV?

Before I begin explaining why the summer and fall may be wetter than normal, I need to explain La Nina, El Nino, and ENSO.

La Nina:

Typical conditions during a La Nina episode.

La Nina and El Nino are part of an oscillation in the central Pacific Ocean called El Nino Southern Oscillation (ENSO).  Ocean temperatures are taken daily to measure the effects and status of ENSO. From the end of 2010 to the beginning of 2012, La Nina has dominated the overall weather pattern.  The picture above shows the typical pattern of La Nina over the south-central Pacific Ocean from December to February.  The Equatorial Thermocline is what causes the ocean temperature differences, and essentially ENSO itself.  During La Nina, the eastern Pacific temperatures are COOLER than normal for at least 6 consecutive months.  This affects the water temperature gradient, which then affects the atmosphere above the water.

Typical La Nina conditions through a year.

The above picture shows the result of an average La Nina around the world during a one year period.

El Nino:

Typical conditions during an El Nino event.

An El Nino episode occurs when eastern Pacific temperatures are WARMER than normal for at least 5 consecutive months.  Notice that the Equatorial Thermocline is deeper and more straight, when compared to a La Nina episode.  So what happens during the rest of the year during an El Nino episode? Take a look

Typical El Nino conditions through a year.


So What Does This Have To Do With The Valley & South Texas?

With La Nina weakening, ENSO conditions will become more neutral, at least until mid to late summer (image below).  Then, conditions will begin to favor an El Nino episode.

Probabilistic ENSO Forecast for 2012.
Courtesy: IRI & CPC

Having said that, hurricane season is just around the corner (June 1st – November 30th).  El Nino typically means a more active Pacific hurricane season and a less active Atlantic hurricane season. For more information on why, click here.  This year, the Pacific hurricane season is predicted to be more active than normal because of the transition into El Nino, according to climatologists.  If this does occur, more moisture will be able to be transported from the eastern Pacific Ocean into Mexico and south Texas.  Tropical cyclones revolve, or spin, counter-clockwise both at the surface and mid-levels of the atmosphere.  If one were to hit the western coast of Mexico, the mid-level flow would transport more moisture over the mountains of the Sierra Madre and into deep south Texas.  This does NOT mean that south Texas would get the full effects of a tropical cyclone.  All of the heavy winds and very heavy rain would be hindered by the mountains in Mexico.  The Valley would end up seeing more stratiform, or non-convective, rain, theoretically.  This is why I PREDICT a “wetter than normal” summer/fall and maybe even winter 2012.


About Brian

University of Oklahoma graduate with a degree in Meteorology. Follow me on Twitter: @WeatherInformer
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