Archive for Drought

Is there an El Nino in the cards for 2012? Perhaps, but not looking as likely.

The mark of a busy hurricane season usually has one element missing from it: El Nino. That is to say, El Nino conditions in the Tropical Pacific tend to suppress Atlantic hurricane activity. This is due mainly to strong upper level winds that cut across the breeding grounds for hurricanes, thus limiting their numbers and intensities. However, one must remember infamous exceptions to this rule such as Andrew in 1992, an El Nino year. There are others as well which remind us of the adage “it only takes one”.

What about neutral years? What defines a neutral year anyway? Basically, when we see the sea surface temperature (SST) anomaly in the Tropical Pacific between .50 Celsius above or below normal, it is a neutral year (ENSO neutral). The scale is not tipped in one direction or another. Easy enough, right?

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Big time rains for the southern states

HPC 5-Day QPF

HPC 5-Day QPF

Get ready for some rain! If you live in eastern Texas, Arkansas and indeed a good deal of the Deep South, you’re in for some wet weather over the next five days. Take a look at the HPC QPF map. It shows the forecast precip over the next five days and a lot of it! The culprit? A potent upper level storm system now situated over southern Arizona and moving in to New Mexico. It will tap the warmer-than-normal Gulf of Mexico moisture supply and really ignite as we continue to move through the week.

While rainy, nasty weather is usually not a welcome event, in this case, I think people will be pleased to see it because of the drought relief it will bring.

U.S. Drought Monitor Map- Sept. 13, 2011

U.S. Drought Monitor Map- Sept. 13, 2011

The last few years have been exceptionally dry for the southern Plains and especially Texas. Looking at the U.S. Drought Monitor maps we can see that at the peak of last year’s hurricane season (Sept. 13 map), nearly the entire state of Texas was experiencing exceptional drought conditions. I have little doubt that this was the reason why TS Don literally dried up as it made landfall in south Texas in July. In fact, the air mass over the western Gulf remained very dry for a bulk of the hurricane season. When TS Lee formed in early September, it too entrained the bone-dry air over the region and actually transformed in to a sub-tropical storm, losing its purely tropical characteristics. I call this phenomenon the Texas Air Layer, similar to the Saharan Air Layer which can dominate the tropical Atlantic with dry, stable air.

Now let’s fast forward to the current winter pattern. We have seen quite an increase in rain fall over a significant portion of Texas and surrounding states due to a favorable storm track and possibly a warmer than normal Gulf of Mexico which supplies more moisture for storm systems. It has also been warmer than normal for the region as it has been for much of the Southeast. This is partly due to a positive NAO or North Atlantic Oscillation which has kept the deep east coast troughs which usher in Arctic Air at bay. Instead of prolonged periods of cold, dry air, the Arctic attacks are brief and the result has been a warmer, wetter winter for much of the southern tier states.

U.S. Drought Monitor Map- Jan. 17, 2012

U.S. Drought Monitor Map- Jan. 17, 2012

You can see the resulting improvements on the latest Drought Monitor map labeled January 17. A remarkable change to say the least and more rain is coming which will further knock down the dry conditions for Texas and elsewhere.

My theory is that if this pattern continues, perhaps the air mass over the southern U.S. and adjacent Gulf Waters won’t be as dry this hurricane season. If this is the case, maybe, just maybe it would open up the western Gulf, Texas included, to more tropical cyclone activity. It makes sense to some extent: if the abnormally dry air mass is gone, due in part to a wetter land mass underneath, then it stands to reason that approaching tropical cyclones won’t dry out nearly as much as we saw in 2011. I think we can all agree that watching Don erode away to nothing as it made landfall was one of most incredible demises to a tropical storm that we’ve ever witnessed. It provided next to no rain fall for the region that it impacted and was all but gone in less than 24 hours after landfall.

We’ll see how this all plays out for the upcoming hurricane season. It may have no bearing at all but I think that drought begets drought and thus more dry air; a kind of feedback mechanism. We know that tropical cyclones are incredibly sensitive to dry air and what we saw over the western Gulf last season was enough to keep the region well protected. I’ll keep tabs on the Drought Index and post a follow up report in the early part of June. For now, enjoy the abundance of rain fall but be mindful of the hazards that excessive rains can bring. It’s all good until somebody gets hurt and we don’t want that.

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