If you've been paying any attention to the national weather lately, you without a doubt have Tropical Storm (soon to be Hurricane) Isaac on your mind. You may also have the Global Forecast System (GFS), European Center for Medium-Range Weather Forecasts (ECMWF), Hurricane Weather Research and Forecast System (HWRF) and various other alphabet-weather models fluttering through your brain.
The national media have been discussing them ad-nauseum. The controversy and hype surrounding these computer models almost eclipse Isaac itself at this present time.
It's understandable to be drawn into the sea of model interpretation with a tropical system. After all, the subsequent track and intensity forecast by these computer models are paramount. I'll resist doing so in this blog, and instead address the prospects of Isaac directly affecting Oklahoma. By doing so, I'm going to delve into the model madness – it appears my hypocrisy knows no bounds!
Regardless of which computer model you glean your information from, Isaac is still at least four days away from the Sooner State. The variance in forecast track of the center of circulation of Isaac at 96 hours out is hundreds of miles. This means by Friday the remnants of Isaac could be anywhere from McAlester, Oklahoma, to Little Rock, Arkansas, to Nashville, Tennessee. This is the inherent nature of any dynamical, statistical or consensus based computer model: the farther out in time the model runs the lesser the degree of accuracy.
With the westward trend of the historically more accurate models, as well as current observations, my confidence in the remnants of Isaac bringing tropical moisture and rain to at least eastern Oklahoma is slightly higher than what it was a few days ago. Amounts could be anywhere from a few tenths of an inch, to several inches given the tropical nature of the system. The timeline for this would be Thursday night through Friday.
Unfortunately, there is less of a chance of rain from Isaac affecting central and western Oklahoma. Still, increased cloud cover and brisk north winds will be felt late this week as the remnants of Isaac pass to our east.
Human forecasters can compensate for a decline in model accuracy with respect to time by knowing which models have performed well in the past given similar atmospheric and environmental conditions, and applying that knowledge and experience to present day conditions. Certain models are of a higher resolution enabling the potential for greater precision, accuracy and consistency. Other models were programmed specifically for certain types of weather phenomena, i.e., mesoscale, tropical, global. Knowing these things, combined with years of experience, gives the human forecaster an edge that any model alone lacks.