The Art of Dredging

Dredging and shipping

Two typhoons

 

This article is meant for everybody who still believes in fairy tales, and the fact that tropical cyclones always track according to the same template; are born in the sub-tropics, go slowly northwest, recurve and move northeast, faster, until they die in higher latitudes.

 

Here is a “normal” tropical cyclone track (typhoon “Songda”, 2004) recurving back east over Japan.

 

 

 

In October , the Philippines were ravaged by supertyphoon “Parma” .

“Parma” did something entirely else:

 

 

 

On its approach to the Philippines, this typhoon tracked straight Northwest.

Once it made landfall, the whole thing went berserk. It tracked up and down North Luzon for three (3 !) times, back and forth like a merry-go-round,  flooding large parts of the island with heavy rains,… before stampeding off into South China sea.

 

Less harmful was “Lupit”, first projected to hit the same area, a week later. Winds were forecasted to be 185 km/h. Note the yellow  “Potential Track Area”.

 

A few days later the track forecast looked like this:

 

Th Potential Track Area  became. The accompanying notes on the forecast read:

 

MODELS PERSIST WITH A STRONG RECURVATURE SCENARIO

TO THE NORTHEAST WITHIN THE NEXT 12 TO 24 HOURS. THE CURRENT FORECAST

REMAINS CONSISTENT WITH PREVIOUS FORECAST PHILOSOPHY REGARDING THE

MODELS NOT HANDLING A WEAK STEERING ENVIRONMENT ACCURATELY AND WITH

ANALYSIS NOT SHOWING A CLEAR PICTURE OF THE SYNOPTIC STEERING FLOW...

 

If we translate that: computer models show the typhoon to recurve, but cannot be trusted in this case, where no real steering elements affect the typhoon track. The typhoon track became random and unpredictable.

Say again:  nobody knew for sure where this tropical system woud turn to next…

Look what the different track forecasts of the different weather agencies looked like at that moment: the forecasted track directions differ by 140 degrees !  Nobody agrees with one another where this system goes next...

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A few forecasts later, the whole thing did what it was supposed to do, turn northeast and go extratropical.

 

 

Conclusions:

1.       Use more than one source of typhoon track forecasts.

2.       Tropical cyclone tracks are not yet completely understood by meteorologists.

3.       And yep:  sometimes tropical cyclones come back.

 

 

Marc Van de Velde,

October 2009

 

 

 

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