At 5 a.m. Thursday, Hurricane Joaquin had sustained winds of 120 mph and a central pressure of 948 millibars. Further intensification is expected in the short term; the National Hurricane Center is forecasting that Joaquin will strengthen into a Category 4 with winds of 140 mph on Friday and Saturday as it tracks north toward the East Coast.
In their 5 a.m. update, the National Hurricane Center’s forecast track had shifted slightly east, noting that their forecast remains similar to earlier today and is slightly east of model consensus. Additionally, hurricane watches may be hoisted for the United States on Thursday evening.
[What Hurricane Joaquin might mean for the D.C. region]
Hurricane warnings are in effect for the Bahamas, where Joaquin will continue to linger and intensify over the next 48 hours.
Regardless of an exact track, moisture associated with Joaquin will get pulled into an advancing low pressure and almost certainly deliver dangerous amounts of rain over the eastern United States, from the Carolinas to Maine.
Joaquin has the potential to be a very significant storm for the Mid-Atlantic and Northeastern states. Heavy rain will be the first threat to the region on Thursday and Friday. The latest guidance from the National Weather Service includes an enormous swath of rainfall totals in excess of 6 inches over the coming week, with as much as 10 inches falling on the Virginia, Maryland and Delaware coasts.
By Saturday, coastal erosion and storm surge flooding could become a huge problem starting in the Carolinas and working its way up to New England by Sunday.
The most recent wave forecast from NOAA shows significant heights higher than 30 or 40 feet on Sunday — a very ominous scenario. Even if the storm center remains offshore, or it begins to transition to a nontropical cyclone, strong onshore winds will generate substantial storm surge flooding along the coast, particularly during the regular astronomical high tides.
Over the past 24 hours, the vertical wind shear that was keeping Joaquin at bay has gradually decreased, and the storm was quick to respond. The peak winds increased from 40 mph on Tuesday morning to 80 mph on Wednesday morning. The very warm ocean water under it is also undoubtedly fueling the hurricane. Environmental conditions are expected to remain favorable for Joaquin to intensify until Saturday, with a window for rapid intensification now through Friday.
Joaquin has been moving slowly and is forecast to drift to the southwest for another two days before getting picked up by the trough moving over the East Coast. At that point Hurricane Joaquin will head north, but there is great uncertainty in the details of how that will happen.
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Some models suggest Joaquin will turn quickly to the north and then curve toward the East Coast, while others push the hurricane out into the Atlantic and away from land. The uncertainty in track forecast right now cannot be overstated, and it is not even represented well by the official track forecast by the National Hurricane Center. Unfortunately in this situation, the spread in the forecast models is far greater in size than the cone of uncertainty in the official forecast.