Isaac remains a tropical storm as it skirts northern coast of southeast Cuba

This afternoon, Isaac remains a tropical storm with little change in intensity as it moves northwest along the northern coast of Cuba, with winds of 60 mph. The storm's center is currently skirting the northern coast of southeast Cuba over the state of Holgiun. There is a hurricane hunter mission currently flying through the storm. The hurricane hunter mission and recent satellite images show that Isaac has maintained its core circulation, providing a launching point for new thunderstorm activity to develop. Isaac's strongest thunderstorms, which were on the southeast side of the storm just south of Hispaniola, have weakened somewhat this afternoon, as stronger thunderstorms begin to develop north of Cuba. A new burst of convection above the storm's center of circulation also began this afternoon. Upper level outflow is strong on the north and northeast side of the storm, though is weak and disorganized on the south and southwest. Wind shear around the storm remains 10-20 knots.


Figure 1. Satellite imagery of Tropical Storm Isaac as it moves northwest along the northern coast of Cuba on Saturday afternoon.

Impacts:
Heavy rain continues over Hispaniola this afternoon as the center of Isaac moves away from Haiti. Once person is confirmed dead in Haiti today as a result of Isaac and its torrential rain and flash flooding, though there are reports that up to three are dead in the earthquake and cyclone-ravaged state. Rainfall totals up to 12 inches are possible in Hispaniola when it's all said and done, with local amounts up to 20 inches, especially in the higher elevations of the mountains. Thousands of people have been displaced due to damage to their less-than-substantial tent structures, and schools and other more sturdy buildings have been opened for shelter while the storm continues to produce heavy rainfall over Hispaniola. Rain has begun to fall in the Florida Keys as the storm's far northern thunderstorm activity moves toward the state. Governor Rick Scott has declared a state of emergency for the entire state of Florida in preparation for the impacts of Isaac. The Republican National Convention has at least one attendee backing out so far: Alabama governor Robert Bentley has decided to stay in-state as Isaac approaches. Vice President Joe Biden has also canceled his trip to Tampa which was scheduled for next week alongside the Convention. Amtrak has also shut down part of their Silver Service line from Miami to Orlando.

Track forecast:
The GFS and CMC are favoring a track to the Mississippi/Alabama border this afternoon, while the GFDL, HWRF, and ECMWF are all forecasting tracks into the Florida Panhandle. The National Hurricane Center is in agreement with the latter forecast, though it's important not to focus on the center of the forecast track. Tropical Storm Isaac is expected to continue to skirt the northern coast of Cuba throughout the rest of Saturday, at which point it will cross the Florida Keys likely on Sunday, late afternoon. From there, Isaac is expected to move northwest until Tuesday when it will make a slight turn to the north. Landfall in the models has been coming sooner and sooner over the past few days, and is now expected Tuesday evening.

Intensity forecast:
In addition to the warm water that Isaac will continue to traverse over the next few days, recent model runs suggest that when Isaac leaves Cuba and enters the Gulf of Mexico, it will be in an environment favorable for intensification. Both the GFS and the ECMWF have been forecasting a large upper level anti-cyclone, or "high," over Isaac as it tracks north through the Gulf. Also, surrounding the upper level high, there are several upper level "lows," that could act to siphon this air away from the storm quickly. These features would provide strong ventilation of the storm, which will likely enhance intensification. The GFDL and the HWRF are in agreement this afternoon that Isaac is likely to reach or come very close category 2 hurricane strength with winds around 95 mph by the time the storm reaches the northern Gulf Coast. The National Hurricane Center is forecasting Isaac to reach category 2 status by 2pm EDT on Tuesday. Given the evidence, I agree with this, and will go a step further to say that a major hurricane (category 3+) is not out of the question, nor is a rapid intensification. Lots of uncertainty remains as Isaac treks across northern Cuba. So many things depend on what form this storm will be in once it leaves that coast for the warm Gulf of Mexico waters.

Portlight gears up for Isaac

Our friends at Portlight Strategies are gearing up for Isaac as we speak. From their blog this afternoon: "John Wilbanks, a long time Portlight member and instrumental in many of the things we do will be heading to Panama City tomorrow afternoon along with a team from Yankee 1, a relief organization made up of retired miltary to provide relief services and SAR if that becomes necessary. John's website, Stormjunkie.com, will be streaming video of operations in the strike zone; you can see what Portlight's teams are doing here. We are also reaching out to the disability community in Haiti and rekindling old relationshps there in the aftermath of Isaac's passage of that island. With over 300,000 still displaced after the earthquake of two years ago, the need there will be great."

You can donate to Portlight's disaster relief fund here.

I also wrote a somewhat applicable blog this morning about model uncertainty in hurricane forecasting.

Angela