The Art of Dredging

Dredging and shipping

TROPICAL CYCLONE AVOIDANCE

 

RULES OF THUMB 

 

Seafarers all over the world still abide by prehistoric techniques to avoid a tropical cyclone (TC).

.

 

I remember I learned this rule-of the-thumb:

 

Question:  “What is the tropical cyclones season. ?”

 

Answer: “Juin, too soon, “

              “July standby, “

                                    “August don’t trust, “

                “September remember,”

                    “October, all over. “

 

And good luck to you, mariner, who may run in a hurricane in the Atlantic late December, or an early typhoon in April in the Northwest Pacific, to find out that this mantra is not true.

 

Another deadly dogma is the idea that all tropical cyclones recurve halfway their track.

 

 

 

 

 

 

 

 

Recurving track of tropical cyclone "Tip", 1979.

 

 

 

 

 

 

 

 

 

 

Contrary: not all tropical cyclones recurve, about 30 % do not recurve at all, but follow all kinds of random tracks, and can behave erratic and highly inpredicatble.

 

Just check out this inside illustration from NOAA: it shows possible cyclone tracks.

Few of them are the "classic" recurving track we've all learned at school.

Textbooks give the statistical mean track.

But around 30 % of cyclones deviate from those statistics and follow all kinds of unexpected tracks.

 

 

 

ASK YOUR BAROMETER

You know “pressure riding”, don’t you ?

           

A ship sails in the vicinity of a tropical cyclone, checking out the barometer reading continuously.

 

When the barometer drops, the ship sails a different course until the barometer rises again. Thus, the ship keeps a “safe” distance from the tropical cyclone

 

Now watch here typhoon “Zoe”, december 2002 in the West Pacific:

 

 

Imagine you’re following this cyclone, pressure-riding, when –suddenly and unexpectedly- this hurricane turns back in his tracks and gives you a rogue 48 hours.

Think you’ll notice timely when “Zoe” reverses and comes down your ship with a speed of 20 knots ?

Well, “Zoe” is not exceptional,  not at all.

 

What’s your ship’s speed ?

And do you know what course you'll follow to evade this hurricane ?

And where is the damn’ thing heading at next, anyway ?

Ask your barometer, you said ???

 

You’re probably gobbled up by hurricane “Zoe” before you come up with some answers.

 

And remember; it’s december.

 “Zoe shouldn’t have been there in the first place !

 

1 - 2 - 3 - SYSTEM

Heard of the 1-2-3 system ?

Read it here: http://kennebeccaptain.blogspot.com/2008/05/guidelines-for-avoiding-hurricanes-at.html

 

 

 

 1-2-3-system

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Must read in this context: http://www.nhc.noaa.gov/HAW2/pdf/marinersguide.pdf

(Mariner's Guide for Hurricane Awareness in the North Atlantic Basin")

You have to reckon that the cyclone will cooperate !

The 1-2-3 system assumes that the cyclone will follow the textbooks.

Here is something new: tropical cyclones do not read textbooks.

And the chances you take (by assuming that cyclones stick to the rules) are huge.

Guessing that cyclones will follow the rules is close to a game of Russian roulette.

 

Pressure riding, forecasting a cyclone by observing wind and barometer,  rules-of thumb; it’s all something like sending a myopic into a lion’s cage.

It’s old school.  And it’s dangerous.

 

You’re already dangerously close to a tropical cyclone, when you notice the drop in barometer readings, or the long swell, and you probably have no clue where the tropical cyclone will move next, especially if it moves on an irregular track.

 

With modern forecasting and communication techniques, satellite imagery, raw computing power used for cyclone forecasts, etc… no ship should go close to a tropical cyclone, with only the barometer to keep the ship out of the storm centre.

 

A ship can and should stay at an arm’s length or more from a cyclone and enjoy a much wider safety margin, than in the old days.

 

Anyone who has ever seen the inside of tropical cyclone can tell you that sailing into a severe cyclone is NO option.  

 

Weather forecasting onboard should move on beyond the barometer and the windvane, and use modern ways to get meteo-data onboard.

And ships should use the modern techniques available to keep a wider safety margin between the ship and a tropical cyclone.

 

Captains should use their overriding authority to enforce this wider safety margins, not giving in to “pressure from the head office”, real or perceived.

 

Frankly, I don’t understand why some captains take their ships voluntarily close by or inside a tropical cyclone.

A tropical cyclone can speed up, trapping the ship in an much more powerful system than expected.

Or the cyclone can change its track, setting the ship in the dangerous semi-circle.

 

All stakeholders involved should realize that a tropical cyclone is a natural disaster, nothing less, and not something to be taken lightly. 

 

 

Marc Van de Velde

Note: this website contains topics on how to receive weather data onboard.

 

LINKS 

http://www.nooa.gov/                                                      NOAA

https://metoc.npmoc.navy.mil//jtwc.html                          Joint Typhoon Warning Center

http://www.typhoon2000.ph/        A amateur site, with an email early-warning for typhoons.

http://www.weather.org.hk/marine.html                             Marine Weather Hong Kong

http://www.jma.go.jp/JMA_HP/jma/indexe.html                 Japan Meteorological Office

http://www.franksingleton.clara.net/gmdss_links.html        GMDSS warnings by Navarea

http://www.ndbc.noaa.gov/cgi-bin/map_search.pl             Buoy-weather

http://www.metoffice.gov.uk                                             Homepage UK Met. office

http://www.ecmwf.int                         Europees center for weather model forecasting

http://www.weather.org.uk/models.htm                             Numerical weather models

http://www.nrlmry.navy.mil/pubs.htm                                Valubale and accesible info

http://www.users.zetnet.co.uk/tempusfugit/marine/

 

Subscribe to our newsletter:

Write us:

reply.to.artofdredging (at) gmail.com



Manu's scripts

- a sailor's fifth column