The Art of Dredging

Dredging and shipping

M/V "Princess of the Stars"   -   Was it inevitable ?

On Juin, 21, 2008, M/V “Princess of the Stars” a passenger ferry, capsized in typhoon “Frank”, off Rombon, Philippines. 

The story carries all the ingredients of a tragic mistake.

The captain either did not use his overriding authority and sailed his ship from Manila, with this typhoon building up in the south.

Either he was unaware of last-minute changes in the prediction of this typhoon (a common mistake), or his equipment failed, so he did not get the weather data in time. Or somebody failed to get the data through.

Somebody, somewhere, somehow made a mistake.

The operator of the ferry "Sulpicio Lines" blamed the Philipine Coastguard,  PAGASA, the ship's captain, the weather, and God's Will. Apparently not themselves.

The ship probably suffered engine breakdown, grounded, was holed and capsized.

About 800 passengers and crew died.

Why ?  And foremost: was it inevitable ?

This is the 21st century, typhoons can be predicted -to a certain level- , and there is no reason to take a ferry straight in the path of a typhoon.

Predictability of tropical cyclones

Tropical cyclones are predictable, up to a certain level….

This article will poke further in this issue; how much can you trust a tropical cyclone track forecast, knowing that the safety of your ship and crew may depend  on it ?

I will use here the track of typhoon "Tip" as an example.  "Tip" is the strongest tropical cyclone on record. 

A tropical cyclone is born (1) , organises (2), gets underway (3), recurves (4) and becomes extratropical (5). 

 

Numbers on the picture above are explained beneath, with an assessment of predictability of a cyclone in each stage of its life.

"1":  A tropical cyclone is born in a patch of warm ocean water, in a disturbed air circulation.

In this stage tropical storms (TS) are very hard to detect, let alone predict their future track. 

TS's are mostly born in ocean regio’s where very little meteo data is gathered (West coast of Africa, East of the Philippines, etc…).

Startup cyclones may only be detected with infrared and visible satellite imagery. And at this stage they do not have the characteristic “eye”, which would make them easier to pinpoint.

Predictability: poor

"2": The tropical cyclone wanders around for a few days, gathering strength, getting organized in a cyclonic pattern.  There is still no definite direction in its movement.

Tracks are still hard to forecast. It’s even hard to forecast if the tropical storm will develop in a full blown cyclone or not.

Predictability: poor, becoming fair

"3": The tropical cyclone finally chooses a direction.

The track is pretty well predictable for the next days; the eye is well defined and can be easily followed by satellite, the track direction and speed is more or less steady.

Predictability: fair to good

 

"4": Recurving.

Well, most cyclones recurve, obeying simple physical rules. Others do not, obeying exceptions to these rules.

Here are two chart of hurricanes in the North Atlantic and NW-Pacific, year 2007.

As you see: not all cyclones recurve, some go straight on, some follow erratic tracks.

And some trpoical cyclones recurve… but NEVER count on it.

Weather forecasters name this one of the biggest challenges in forecasting today: whether or not a cyclone will recurve.  And very often they got it wrong. 

Predictability: poor

 

"5": Extratropical: cyclones become extratropical in higher latitudes, speeding up to 30-50 knots. They are dying fast in higher latitudes, because of the lack of warm water underneath.

But they can be especially dangerous in their dying hours.

An extratropical cyclone can cover 2000 miles in 48 hours. Every small error in forecasted track direction can cause an extratropical to appear where it is least expected, causing damage and ship loss. The speed with which extratropical cyclones can strike is incredible, and leaves no time for the unprepared.

Extratropical cyclones are basically unguided missiles.

Predictability: poor, especially in direction

Remember:

Faulty cyclone forecasts may be more likely during :

  • birth of a tropical storm, and first days of formation of the system
  • recurvature
  • extratropical trangression, up to end of lifecycle

Conclusions

      1.    Do not blindly trust tropical cyclone forecasts.

2.     Surely do not blindly trust one source of forecast only .

3.       Do not engage in wishful thinking.

      “Oh well, I guess  this cyclone will recurve, no problem to us.”

4.       Get to know your dredging site, from a meteo point of view,  especially if you are in a known area of tropical cyclones.           Be prepared.

      Check out specialised info, for example:

         North-Atlantic: http://www.nrlmry.navy.mil/port_studies/tr8203nc/0start.htm

         NW-Pacific:     http://www.nrlmry.navy.mil/port_studies/thh-nc/0start.htm

      Both sites give the experience of the U.S. Navy with most harbours in both regions, concerning their suitability as cyclone shelter. The U.S.Navy operates some 50+ years in these regions, and their experience is profound.

  

 

Marc Van de Velde

Subscribe to our newsletter:

Write us:

reply.to.artofdredging (at) gmail.com



Manu's scripts

- a sailor's fifth column