Category 3 Joaquin Bears Down on Bahamas

Hurricane Joaquin got down to business on Wednesday afternoon, vaulting from Category 1 to 3 status in a mere six hours. Joaquin’s top sustained winds zoomed from 85 mph in the 21Z (5:00 pm EDT) advisory from the National Hurricane Center to 115 mph in the 11:00 pm EDT advisory. Since the top winds were only 70 mph on Tuesday night, Joaquin more than qualifies for rapid intensification by the NHC’s definition: an increase in sustained winds of at least 30 knots (35 mph) in 24 hours.

Joaquin is now the second major hurricane of the Atlantic season, joining Hurricane Danny and beating the expectations of seasonal forecasters, as recently as early August, of just one major hurricane in the Atlantic this year (though Danny barely qualified as a major, with winds above that threshold for only a few hours). The current total of 10 named storms is also near the top end of seasonal predictions.


Figure 1. Latest satellite imagery of Hurricane Joaquin from the WU tracking page.

Joaquin still lacks a crisp, well-defined eye on infrared satellite imagery, but its showers and thunderstorms have continued to intensify and consolidate into a large and increasingly symmetric central core. Hurricane-force winds remain confined to a radius of 35 miles from the center of Joaquin, while gales extend out up to 140 miles. The most recent minimal central pressure was 951 millibars, a hefty drop of 37 millibars in roughly 18 hours. Very warm sea-surface temperatures of around 30°C and relatively deep ocean heat content will support even more strengthening over the next couple of days. Hurricane warnings are in effect for the central and northwestern Bahamas, with a hurricane watch for Bimini and Andros Island and a tropical storm warning for the southeastern Bahamas and Andros Island. My Wednesday afternoon update with Jeff Masters has more detail on potential impacts to the Bahamas from this formidable hurricane.

Moderate northerly shear will relax significantly on Thursday into Friday, and it’s possible that Joaquin will have outflow jets helping to ventilate the storm on both its west and east flanks. Together with record-warm SSTs, these factors could help make Joaquin a dangerous Category 4 storm, in line with the latest NHC outlook, which produces peak sustained winds of 140 mph on Thursday night.


Figure 2. Upper-level winds above roughly 35,000 and 55,000 feet (blue flags) show an anticyclonic outflow signature developing over Hurricane Joaquin at 03Z Thursday, October 1 (11:00 pm EDT Wednesday). An outflow jet with wind speeds above 50 knots (58 mph) is funneling from Joaquin toward the southeast, helping to ventilate the storm. Image credit: SSEC/University of Wisconsin.

Some weakening is expected when strong upper-level southerlies begin to impinge on Joaquin’s circulation, especially over the weekend, but Joaquin is likely to remain a potentially damaging hurricane, with a gradually enlarging envelope of high wind, high seas, storm surge, and heavy rain.


Figure 3. Comparison of model projections for Joaquin from 12Z Wednesday. The ECMWF run stands in stark contrast to all other model runs, which are clustered far to the left. The official NHC forecast from Thursday morning (magenta line) splits the difference somewhat. Image credit: Stu Ostro, The Weather Channel.

Forecast update
As we discussed on Wednesday afternoon, most of the computer model runs from 12Z Wednesday pointed toward a landfall for Joaquin somewhere along the coast of North Carolina or southern Virginia. Only the operational ECMWF remained an outlier, taking Joaquin far to sea.

The 18Z suite of guidance did little to change this picture: no ECMWF runs are produced at 18Z, and the other models continued to insist on a U.S. landfall. Early guidance from 00Z Thursday (produced by injecting the most recent data on Joaquin into the 18Z Wednesday model runs) showed little track change, although the projected intensity at landfall is now considerably higher because of Joaquin’s current strength. The complete suite of runs from 00Z Thursday—and in particular the ECMWF run—may help clarify Joaquin’s future, unless of course the ECMWF sticks to its out-to-sea story. The 00Z GFS track was considerably to the right of previous runs, taking Joaquin toward New York and New England, so it appears the picture may remain far more complex than forecasters and residents would prefer.

Most of the dozens of GFS and ECMWF ensemble runs from 12Z Wednesday showed a U.S. landfall, despite the operational ECMWF’s contrariness. (Ensembles are produced by running a model many times, each with slightly different initial conditions to represent uncertainty in the atmosphere’s starting point.) Until we know more, the out-to-sea depiction of the highly skilled ECMWF model must be considered a possibility, as Jeff Masters noted in his WUTV segment on Wednesday evening. At the same time, U.S. coastal residents will need to be getting ready on Thursday for quick action, as it’s possible that a hurricane watch will be posted by NHC as soon as Thursday evening. As of 11:00 pm EDT Wednesday, the official NHC track brings Joaquin into the Delmarva region late Sunday into early Monday.

Jeff Masters and I will have our next update by midday Thursday. We've also launched a live blog on Hurricane Joaquin that will feature updates in between our blog posts.

Bob Henson