As expected, the vigorous tropical wave off the African coast has been designated Tropical Depression Four as of 11:00 AM EDT. It “could become a tropical storm during the next 24 hours,” but initially at least, strengthening will likely be slow due to wind shear today and tomorrow. There’s even a chance, as Eric Berger points out, that it could fall apart. But if it holds together until the shear abates, then it could be Katie bar the door:

THE EASTERLY WIND SHEAR WILL PROBABLY LIMIT INTENSIFICATION DURING THE NEXT COUPLE OF DAYS. THEREAFTER…THE GLOBAL MODELS…EVEN THOSE THAT DO NOT HAVE A STRONG REPRESENTATION OF THE TROPICAL CYCLONE ITSELF…FORECAST AN UPPER-LEVEL RIDGE TO BUILD OVER AND NEAR THE LESSER ANTILLES. COMBINED WITH WARM SEA-SURFACE TEMPERATURES ALONG THE TRACK…CONDITIONS APPEAR CONDUCIVE FOR STEADY STRENGTHENING LATER IN THE FORECAST PERIOD.

Of course, if those conditions actually materialize — low wind shear, high SSTs, and no other inhibiting factors like dry air or Saharan dust — the intensification probably won’t be “steady,” it’ll probably be rapid. Given the inherent limitations of intensity forecasting, the NHC would never predict such an eventuality this far in advance… but Alan Sullivan would, and does: “When the easterly sheer quits kicking its butt, rapid intensification is probable.”

In the discussion, the NHC points out, “IT IS IMPORTANT TO REMEMBER THAT SIGNIFICANT UNCERTAINTIES EXIST IN BOTH THE TRACK AND INTENSITY FORECASTS…ESPECIALLY AT LONG RANGES.” That’s very true. But it isn’t stopping the weather nerds from speculating. For instance, Berger writes: “[D]ynamics in the upper atmosphere are such that T.D. Four is unlikely to curve poleward any time soon… In other words, the system’s most likely destination now is the Caribbean Sea, where waters are extremely warm.” On the other hand, Sullivan, who lives in South Florida, “think[s] early recurvature is still possible,” but is “also concerned about a mere leftward wobble that gets our storm north of Puerto Rico, followed by just enough building high pressure to head the cyclone west again. This is the Andrew scenario, and it is plausible for this system.” He concludes: “I feel exceptional uncertainty about the future course of our Atlantic cyclone. Destinations from Tampico to Halifax are plausible. The worst-case scenario of a first landfall in South Florida is plausible, too.” For what it’s worth, here’s what the computer models say, out to 120 hours:

Needless to say, it is waaaaay too early to put any stock in any particular forecast “line,” whether from the official forecast track, or from any particular computer model… such as, for example, the GFS, which shows Hurricane Dean moving up the Eastern Seaboard toward New England in 12 days:

What was I saying? Oh, right, don’t take any of these computer models seriously. :) Case in point: just a few days ago, the same GFS model was predicting a New Orleans landfall. (”I’m no Brendan Loy but the GFS does have a Category 2 Hurricane hitting New Orleans on August 23rd,” Jesse Ferrell wrote on Friday. Heh.) So just stay tuned, and if you’re in a coastal area anywhere along the Atlantic or Gulf coasts, brush up on your basic hurricane preparations — the ones that should always be in place this time of year anyway.

P.S. Ferrell points out that it might not be Dean: “Don’t assume that this will be Tropical Storm ‘Dean’ however… it could be ‘Erin’… some models are still talking about the system in the Caribbean becoming a tropical storm this week as well.”

P.P.S. Ferrell has added an update, pointing out the same thing I did: “The GFS now has the hurricane hitting New York City, after three consistent model runs hitting the Texas Coast.”

UPDATE: Dr. Masters has posted an update, in which he writes of T.D. 4’s future:

The total heat content of the ocean stays relatively low through the next 48 hours (Figure 1), so no rapid intensification is likely until Thursday, when the storm approaches the Lesser Antilles Islands. The 12Z (8am EDT) run of the GFDL model intensifies TD 4 into a Category 2 hurricane five days from now. …

The big question is how strong the trough of low pressure predicted to pass north of TD 4 on Friday will be. If the trough is stronger than currently forecast, it may be able to pull TD 4 far enough north so that it misses the Lesser Antilles. This would be good for the islands, but potentially bad for the U.S. East Coast. The trough will likely not be strong enough to recurve TD 4 harmlessly out to sea, and the storm would then be forced westwards again by the next ridge of high pressure. A landfall along the U.S. East Coast as a hurricane–possibly a major hurricane–could result, unless the next trough of low pressure is strong enough to recurve the storm out to sea. The latest (12Z) run of the UKMET model has TD 4 passing through the very northernmost Lesser Antilles Islands. The 12Z GFDL, GFS, and HWRF have TD 4 jogging just far enough north that it would likely miss the islands. Some of these runs are considerably slower, delaying the possible impact to the islands to Saturday or Sunday. What may happen after 5 days is highly uncertain. Last night’s GFS model run had TD 4 eventually making landfall south of Brownsville, Texas. This morning’s run had it eventually hitting New England–a difference of about 2000 miles in landfall location!