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Bounty (Wikipedia photo) |
Possibly the captain was using traditional low-tech hurricane avoidance techniques that were not applicable to the situation.
From the NTSB report:
A traditional method of hurricane avoidance is to stay a safe distance from the eye on a track that passes the hurricane using the so-called navigable semi-circle.It is possible that the captain may have focused too narrowly on the position of the storm’s eye instead of on Sandy’s total expanse (winds associated with the storm spanned more than 1,000 miles in diameter, and the area into which the Bounty was heading was already under tropical storm warnings, with conditions forecasted to worsen).Still, the captain seemed to believe that he could outrace the storm.
On the navigable side,(the west side in the case of Sandy) as the storm approaches, the winds and seas will be astern (important for a square rig sailing vessel) while also pushing the vessel out of the path of the storm. Also the wind speeds are less because the winds are the cyclonic so the total wind speed is the winds minus the storm direction. On the dangerous semi-circle side (east side) the winds and sea tend to push the vessel into the path of the storm and also the cyclonic winds are added to the storm direction.
It seems plausible that Capt. Walbridge would have had high confidence in traditional low-tech avoidance methods.
The problem is that in the case of Sandy at the time of the encounter the concepts of navigable/dangerous semi-circle were invalid.
This is because when the Bounty encountered Sandy it was transiting from a tropical cyclone(warm core) to an extratropical cyclone (cold core). The meteorology is complex but the take-away for the mariner is that the wind field will expand and the field will no longer have the same characteristics.
Here is tropical cyclone Katrina:
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Katina (From NASA) |
From NASA:
Katrina was a textbook tropical cyclone, with a compact, symmetrical wind field that whipped around a circular low-pressure center.
Sandy, at about the time of the encounter on the other hand looks quite different:
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Sandy (from NASA) |
So when tropical cyclones become extratropical, their wind and cloud fields expand dramatically. Their strongest winds generally weaken during this process, but occasionally a transitioning storm retains hurricane force winds, as was the case with Sandy.
From the NHC on the 28th.
THE MOST RECENT AIR FORCE HURRICANE HUNTER AIRCRAFT MISSION DID NOT
FIND WINDS OF HURRICANE FORCE NEAR THE CENTER OF SANDY.
HOWEVER...EARLIER DROPSONDE DATA INDICATED THAT WINDS TO HURRICANE
STRENGTH WERE OCCURRING WELL TO THE SOUTH AND SOUTHWEST OF THE
CENTER.
FIND WINDS OF HURRICANE FORCE NEAR THE CENTER OF SANDY.
HOWEVER...EARLIER DROPSONDE DATA INDICATED THAT WINDS TO HURRICANE
STRENGTH WERE OCCURRING WELL TO THE SOUTH AND SOUTHWEST OF THE
CENTER.
What the Bounty encountered may have the highest wind speeds in the system. The Bounty was about 100 miles from the center in what would be considered (in a hurricane) the navigable semi-circle. What was encountered instead was not only the highest wind speeds but also the roughest seas, made short and steep by the contrary (north bound) Gulf Stream current.
In spite of the complex situation the models used by meteorologist for the Sandy forecast were accurate. There is a good discussion of the forecast here. Had the captain used the NHC (National Hurricane Center) forecasts he may have been able to avoid the worse of the storm. Of course with few hurricane encounters under his belt the inexperienced Walbridge likely had more confidence in his own skills then the NHC forecasts. Walbridge's confidence was misplaced.
A better approach is to set wind speed and/or sea height limits before the voyage and to use forecasts to ensure those limits are not exceeded.
Even better then dodging bad weather of course to find a good hurricane hole, put out extra lines and stay put till the storm passes.
K.C.
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The NWS warns that the 1-2-3 Rule "does not account for the typical expansion of the wind field as a system transitions from hurricane to extratropical gale/storm." Nonetheless the rule holds up quite well.
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Sandy and the 1-2-3 Rule from David Burch Navigation |