Saturday, July 20, 2013

Strong African Tropical Wave Could Develop Into a Hurricane

A strong tropical wave currently over far western Africa has potential to develop into a tropical cyclone in the open Atlantic basin before possibly attaining hurricane status closer to the Caribbean.

Infrared satellite imagery indicates the presence of a vigorous tropical wave over western Africa. Short range GFS model products indicate this tropical wave will push off into the open Atlantic in the next 72-84 hours, before the first signs of development appear. It appears the system fluctuates in strength after development into a rather weak tropical cyclone takes place in the next week or so.

Pushing ahead into the 10-14 day mark, model forecasts develop the tropical system into a stronger tropical storm or a weak hurricane as the cyclone approaches the Caribbean. Previous forecasts from the GFS model take the system anywhere from scraping the Eastern Seaboard to an entrance into the Gulf of Mexico. Based on climatological tracks from where the tropical wave is now, and the current atmospheric flow for tropical waves and/or tropical systems above the 1000 millibar mark, I find the track towards the Gulf of Mexico more likely. A certain caveat is the potential that the atmospheric flow changes drastically, in which case a different track may be favored. But at this point in time, I am hard-pressed to find another track I find more favorable than at least an entry into the eastern Caribbean.


Text Forecast for August, 2013

This is a text forecast for the month of August, 2013.

After a heat wave across much of the nation in the middle of the month, it is expected that the month of July will be seen as the more intense month when compared to August.

I anticipate the atmosphere to favor high pressure formation across the West Coast into the Rockies, as a rather strong negative correlation exists between June values of the Antarctic Oscillation (AAO), and mid level height anomalies across the Rockies and the West Coast, and even towards New England and the waters off that area. The AAO ended up negative for the month of June, thus my expectation of high pressure formation across the Rockies.

I do expect periodic instances where the high pressure system in the Rockies will propagate into the Plains and possibly eastward into the Ohio Valley. This probability would rise if the New England area also experiences high pressure growth due to the aforementioned negative correlation. 

The Midwest and portions of the Plains will likely endure multiple cool weather periods, as disturbances drop in from Canada and set up a depression in the jet stream that will offer rather enjoyable temperatures in these regions. The passage of cold fronts through these areas also increases the chance of precipitation across the middle of the nation, so it is not a bad idea to believe these areas have a shot at above average precipitation for the month of August.

Primary severe weather event location is expected to stretch from the Northern Plains to the Midwest, as disturbances riding the jet stream will couple with intermittent cold front passages in the Midwest to highlight these areas for severe weather potential. Tornado numbers are expected to end up below average for the month of August, due to a lack of a highly meridional (very wavy) jet stream and displacement of the highest instability to the south of the main upper level flow. Any tornadoes that do occur would be favored in the Northern Plains, at the peak of the jet stream above the high pressure system in the Rockies.

-Forecast Summary by Region-

Precipitation: Above Average
Temperature: Slightly Below Average

Precipitation: Slightly Below Average
Temperature: Slightly Above Average

Precipitation: Below Average
Temperature: Average

South Central
Precipitation: Average
Temperature: Average

Precipitation: Above in north, Below in south
Temperature: Average to Above Average