94L still disorganized; Hurricane Gordon bearing down on the Azores

A tropical wave (Invest 94L) located midway between the Lesser Antilles Islands and the coast of Africa is headed west at 20 - 25 mph. This storm is a threat to develop into a tropical storm that will affect the Lesser Antilles Islands as early as Wednesday. The storm is under light wind shear of 5 - 10 knots, and is over waters of 27°C. A large area of dry air lies just to the north of 94L, as seen on the latest Saharan Air Layer (SAL) analysis and water vapor satellite loops. This dry air is interfering with development, and this morning's visible satellite loop shows that 94L's heavy thunderstorm activity is a bit sparse. The storm does have an impressive amount of spin at middle levels of the atmosphere, though. A pass from the Indian OceanSAT-2 satellite Saturday night at 10:06 pm EDT noted a broad, elongated center of nearly calm winds several hundred miles in diameter at the surface, and nothing resembling a well-organized closed surface circulation. 94L will pass near buoy 41041 on Monday morning. The first hurricane hunter mission into 94L is scheduled for Tuesday afternoon.


Figure 1. Morning satellite image of Invest 94L.

Forecast for 94L
The latest 8 am EDT run of the SHIPS model predicts that wind shear will be low, 5 - 10 knots, and ocean temperatures will be near 27°C through Monday, then warm to 28°C by Tuesday night. As is typical with storms making the crossing from Africa to the Antilles, dry air to the north will likely interfere with development, and the SHIPS model predicts increased dry air as 94L approaches the Lesser Antilles on Wednesday. However, with shear expected to be low, dry air may be less of an issue for 94L than it was for Ernesto or TD 7. Our two best performing models--the GFS and ECMWF--have both been taking 94L through the Lesser Antilles with every run for the past 36 hours. Both models continue to agree on the timing, with 94L arriving Wednesday night or Thursday morning. The BAMM model, which performed as well as the ECMWF and GFS at 5-day forecasts in 2011, is showing a track just north of the Lesser Antilles. Given this agreement among our top three models for long-range forecasts, I give a 60% chance that 94L will pass through the Lesser Antilles. In their 8 am EDT Tropical Weather Outlook, NHC gave 94L a 60% chance of developing into a tropical depression by Tuesday morning. The GFS model has backed off on its forecast that 94L will develop into a hurricane before reaching the islands, and is now predicting 94L will be a tropical storm with 40 - 50 mph winds at that time. The ECMWF model does not develop 94L. It is unlikely that 94L will be able to organize quickly enough to become anything stronger than a Category 1 hurricane before reaching the islands, given the storm's current struggles with dry air, and the lack of model support for intensification. With 94L staying relatively weak and disorganized, the chances of it turning to the northwest and missing the Lesser Antilles, as the NOGAPS model has been predicting, are diminishing. The GFS model predicts that 94L will go on to hit the Dominican Republic as a strong tropical storm on Friday, though the storm could also miss the island, passing just to the north or the south. At longer ranges, the storm is capable of going anywhere from Canada to Mexico's Yucatan Peninsula; it's too early to tell.


Figure 2. The 00Z (8 pm EDT) run of the GFS model from August 18, 2012, was done 20 different times at low resolution using slightly different initial conditions to generate an ensemble of forecasts (pink lines.) The high-resolution operational GFS forecast is shown in white. The GFS ensemble forecast is showing decreasing risk to the U.S. East Coast at long ranges, and an increasing risk to the Gulf Coast.

Gordon bears down on the Azores
Hurricane warnings are flying for the central and eastern Azores Islands as Hurricane Gordon barrels eastwards at 21 mph. Gordon's peak 110 mph winds it had last night made it the strongest hurricane of the 2012 Atlantic hurricane season so far. Latest visible satellite loops show that cold water and high wind shear are taking a toll on Gordon, with the southern portion of the storm deteriorating and the eye beginning to open up. However, Gordon will still be a Category 1 hurricane or strong tropical storm when it passes through the Azores Monday morning. Winds at Ponta Delgada were 11 mph out of the east at 10 am EDT this morning, but will rise through the day as Gordon approaches.

Gordon is not a threat to any other land areas, and the extratropical remnants of Gordon will not bring any strong winds or significant rain to Europe. The last time the Azores were affected by a tropical storm was in 2009, when Tropical Storm Grace brought 65 mph winds on October 4. No significant damage was reported. Ironically, the last hurricane to affect the Azores was the 2006 version of Hurricane Gordon, which caused minor damage in the Azores, consisting of mostly fallen trees and power outages. However, after Gordon became an extratropical low, four injuries due to falling debris from high wind were reported in Spain, and Gordon brought high winds and rain that affected practice rounds at the Ryder Cup golf tournament in Ireland.


Figure 3. MODIS satellite image of Hurricane Gordon taken on Saturday August 18, 2012, at 11:50 am EDT. At the time, Gordon was a Category 1 hurricane with 80 mph winds. Image credit: Navy Research Lab, Monterey.

Jeff Masters

Hurricane