Hurricane Joaquin continues to loom over the Bahamas, making it one of the most devastating hurricanes to hit the Bahamas on record. While the hurricane should miss the East Coast, it will bring heavy rains and possible flooding. Capital Weather Gang's Jason Samenow breaks down what we'll see from Joaquin. (Jhaan Elker/The Washington Post)

Hurricane Joaquin continues to batter the Bahamas as a strong Category 4 storm, but the track forecast has shifted significantly eastward, with no part of the East Coast in the cone of uncertainty. However, although it looks like direct landfall will be avoided, a dangerous rainfall situation is setting up over the Southeast and parts of the Mid-Atlantic this weekend, due in part to the influence of Joaquin.

As of 8 a.m., Joaquin was a powerful Category 4 hurricane with peak winds of 130 mph and a low central pressure of 937 millibars. But last night, Joaquin’s pressure fell to an astonishing 931 millibars — the lowest pressure of any Atlantic hurricane since Igor in 2010.

Hurricane Joaquin has gained a little latitude since Thursday night, and a more rapid motion to the north is expected on Friday. Until then, Joaquin will continue to batter the Bahamas, which have been raked with winds over 100 mph as the most destructive part of the hurricane, the inner core, lingers over the vulnerable islands. The storm rapidly intensified over the very warm waters around the Bahamas, but unfortunately has been adrift in very weak steering currents — as painfully slow 5 mph — leaving it over or very near the Central Bahamas since midday Wednesday.

Flooding rainfall in the Southeast is a significant weekend threat, but forecast models have come into better agreement on a track that keeps the center of Joaquin away from the East Coast. This is reflected in the National Hurricane Center’s official track forecast. Hurricane Joaquin is expected to begin its northward track today and exit the Bahamas on Saturday. It will then follow the upper atmosphere steering currents parallel (but away from) the East Coast.

Joaquin will encounter cooler water as it tracks north, and will weaken steadily over the next five days.


(National Hurricane Center)

Despite Joaquin’s likely track out to sea, the primary impact message remains the same — significant rainfall and flooding is expected in the Southeast. Tropical moisture is streaming off of Hurricane Joaquin and up into the eastern U.S., and that is really bad news for areas that have already received soaking rains over the past week.

Widespread totals over 3 inches are expected up and down the Eastern Seaboard, with over 12 inches forecast in parts of Georgia and the Carolinas, which could lead to dangerous flooding, particularly in South Carolina.

Flood watches are in effect for the Southeast and Mid-Atlantic from Georgia to New Jersey.


Rainfall total forecast through Monday morning. (National Weather Service)

Most models now have Joaquin tracking out to sea, although some models are still hanging on to the idea of a U.S. landfall, including about half of the GFS ensemble members. However, only three of fifty European ensemble members have that solution. The odds are certainly in favor of Joaquin not making a U.S. landfall.


Deterministic and ensemble track forecasts from GFS, CMC, FIM, and ECMWF. (UCAR and ECMWF)

When it comes to steering, a stronger hurricane responds to a deep layer-average wind, while weak storms are steered by a shallower layer closer to the surface. For a storm like Joaquin, a deep layer would be the appropriate choice, and that is shown below. The colored shading is the speed of the steering flow, and the white lines are the directional streamlines. At this point, Joaquin is destined to go north today, forced by the advancing potent trough to its west.


Deep layer mean steering currents on Friday morning. (CIMSS)