Watching former Tropical Storm Dorian wax and wane as it moves westward in the Atlantic north of Puerto Rico got me thinking about this Hurricane Season so far.
Earlier this year all the pre-season forecasters were projecting a busier than average season and in one respect they have been on the mark. To date, we’ve had 4 named storms appear in the Tropical Atlantic Basin. That total is above average for late July. Typically we would have seen 2-3 named storms by the end of July. Only 4 of the 12 past seasons (2001, 2002, 2006 and 2011) have produced that many storms by the end of July. As a side note, 5 of the past 12 seasons saw at least one hurricane by the end of July (2003, 2005,2008, 2010 and 2012).
On the other hand, the storms that have formed have been weak and have struggled to survive. So what gives?
This is where it gets interesting. In early spring, when the first pre-season forecasts were made, there was a large pool of much warmer than normal sea surface water temperatures in the Tropical Atlantic Basin west of the African coast. This was expected to feed systems coming off the African coast. In addition, wind shear was expected to be fairly low, giving tropical cyclones an ideal upper-level environment as well.
This has not happened. In fact, sea surface temperatures in the eastern Tropical Atlantic are now running just slightly above normal, while unusually warm water temperatures have popped up to the north in the Atlantic near Bermuda and northward.
Some forecasters believe that an unusually strong high pressure cell in the Atlantic has sent brisk northeasterly winds to the south off the African coast. This not only has pushed cooler water south into the region, but has also sent dry Saharan air (the SAL, or Saharan Air Layer) into the Atlantic and Caribbean Sea, cutting off the moisture that tropical cyclones need to thrive.
Nobody can say for sure if this will continue through the key months of August and September, but if it does than the pre-season forecast may fall short, though I still expect to see plenty of activity in the region over the next 3 months or so.
Colorado State plans to announce their updated season forecast in a few days. I expect Drs. Klotzbach and Gray to ratchet down their overall forecast a little, though it is safe to say that they will still call for a busy season (based on the development of 4 storms already),
Finally, a quick note about our rainfall this year and our prospects over the next couple of weeks. It appears clear that we are heading back into an extended period of dry weather. High pressure aloft, dry air over the Gulf of Mexico and a lack of tropical will be the main factors in this scenario. The National Weather Service Office in Houston-Galveston produced an interesting series of graphics and where we stand precipitation-wise over southeast Texas. And extended forecasts suggest that we will not see much relief soon.
Such is summer in Texas!