Weather Nerd

Ike rapidly intensifies to Cat. 4; Hanna aims at N.C.

Even as Tropical Storm Hanna made its long-waited northwest turn and took aim at North Carolina for a possible Saturday landfall as a Category 1 hurricane, a more distant but powerful storm, Hurricane Ike, stole the spotlight Wednesday, unexpectedly exploding into a Category 4 monster:

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Infrared satellite image at 11:45 PM EDT. Current loop here.

Ike has 135 mph winds as of 11pm EDT, and a central pressure of 948 millibars — down a whopping 36 millibars in six hours, from the 5pm pressure of 984 mb. To put that in perspective, the standard definition of “rapid deepening” involves a decrease of at least 42 millibars in twenty-four hours. Ike managed almost that amount of strengthening in a quarter of the time.

The NHC discussion states that “SOME ADDITIONAL STRENGTHENING IS POSSIBLE DURING THE NEXT 12 HOURS OR SO,” depending on the timing of any eyewall replacement cycles. After that, wind shear may inhibit further intensification, and perhaps even weaken the system — though the NHC hardly sounds confident of that, saying: “IT IS DIFFICULT TO PREDICT HOW AN INTENSE HURRICANE LIKE IKE WILL BE AFFECTED BY THIS SHEAR.” (Intense hurricanes can “create their own atmospheres” and thus be more resistent to shear.)

In any case, conditions are expected to become more favorable again in 4 or 5 days, as Ike enters the Bahamas, and re-strengthening is expected at that time. The current forecast shows Ike’s peak intensity in 120 hours as exactly where it is now: 135 mph winds.

Where will Ike strike? Well, the current forecast track seems to imply a threat to South Florida, but it’s too early to know. Ike could recurve soon enough to spare the U.S. coast entirely, or it could recurve at just the right angle to threaten someone else along the East Coast — or the Florida scenario could play out exactly as forecast. For now, we wait and see. The odds of a Gulf of Mexico scenario seem to have gone down, at least. But beyond that, it’s hard to predict what will happen.

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Alan Sullivan, who lives in South Florida, wrote this afternoon: “Some models now hint at recurvature off the Atlantic Coast. Let us hope.” He added this evening that, as you can see on the forecast map above, “the course of Ike will supposedly bend back west-southwest, putting it in position to menace Florida. Sometime after that, the real righthand curve will commence. Before Florida, or after? Too early to tell.”

hanna-wedlate.pngAnd what of Hanna? The 11pm discussion calls the storm “a tenacious tropical cyclone,” and notes that it is now strengthening despite some ongoing shear (albeit the shear has lessened somewhat). Tropical Storm Hanna, which the NHC acknowledges “has resembled a subtropical cyclone” at times, is expected to regain hurricane strength, but not to exceed Category 1 intensity.  As for its track:

A NORTHWEST MOTION ShHOULD CONTINUE DURING THE NEXT DAY OR TWO WITH A GRADUAL TURN TO THE NORTH AROUND THE WESTERN EDGE OF THE HIGH. THE TRACK MODELS ARE NOT TIGHTLY CLUSTERED AND THE CONFIDENCE IN THE TRACK FORECAST IS NOT VERY HIGH. HOWEVER…THE MIDDLE OF THE GUIDANCE ENVELOPE HAS HANNA MOVING OVER OR VERY CLOSE TO THE COAST OF THE CAROLINAS. BECAUSE HANNA IS A LARGE CYCLONE…A HURRICANE WATCH WILL LIKELY BE REQUIRED FOR A PORTION OF THE SOUTHEASTERN UNITED STATES COAST EARLY THURSDAY.

Sullivan points out that Hanna is “asymmetrical — serious weather is east and northeast of the center.” As a result, if, as some computer models now suggest, Hanna merely clips Hatteras, it won’t do much damage. “If the center barely reaches the coast, most of that weather will stay at sea.”

FWIW, I have a gut feelng that Hanna will indeed barely reach the coast, if at all. If you look at the forecast graphic archive loop, you’ll see a distinct trend: each forecast seems to be just to the “right” of the previous one. Having grown up watching recurving Eastern Seaboard hurricanes with particular interest because I lived in Connecticut, I learned that, with these storms, you can often learn a lot from the trend in the forecast. That may not be a scientific approach, but if I’m going with my gut, I’m just saying don’t be surprised — the current forecast notwithstanding — if Hanna recurves away from shore and never directly hits anybody, or at worst, clips the Hattears region, with the heavy weather staying out at sea.

Anyway, it’s 2:00 AM and I’m completely exhausted, so I’d better get to bed before I write something incoherent (somefully that hasn’t already happened!). I’ll have more tomorrow on Hanna, Ike and Josephine.

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