Eric Berger, the Houston Chronicle’s official science nerd, has an item in his SciGuy blog today, discussing the current state of the tropics, and why forecasters think activity may be moving closer to our neck of the woods in the next two to six weeks:
Although Hurricane Alex and Tropical Storm Hermine produced some dicey weather conditions in Texas, the United States has been spared a direct strike by tropical weather this year. The biggest storms have formed in the deep tropics and curved north before reaching the Caribbean Sea.
I'll have a story in the Chronicle on Wednesday about why this has happened, but in speaking with ImpactWeather's Chris Hebert this week he told me that pattern may be about to change.
Chris noted that the focus of storm development should shift from the eastern Atlantic to the western part of the basin, including the Caribbean Sea and Gulf of Mexico. Climatologically this also begins to happen during the latter half of September.
One factor that could drive storm formation closer to the United States during the coming few weeks is a shift from "sinking air" in the atmosphere, which dampens thunderstorm activity, to "rising air."
One way to forecast sinking air is to measure the outgoing longwave radiation, the amount of energy leaving the Earth as infrared radiation at low energy. This measurement provides information on cloud-top temperature which can be used to estimate tropical precipitation amounts.
In short, negative values indicate more storm activity and positive values less activity.
The western Atlantic basin has generally seen positive values in recent weeks but as the outgoing longwave radiation forecast maps below show, that should change during the latter half of September and early October.
Climatologists are much better at predicting the chances of short-range weather—which is why you can usually trust your seven-day local forecast and safely ignore the forecast of a coming global climate change catastrophe. If these models are accurate, there could be an increased amount of tropical activity originating and traveling through the Caribbean and Gulf of Mexico.
So far, it’s been a relatively quiet and uneventful season for the Gulf Coast. That might change in the new few weeks. We’ll see.