Archive for the ‘gale’ Category

Sea State: A New But Needed Concept

January 16, 2009



No, the term sea state does not refer to some group of atolls in the Pacific or Indian oceans that comprises a small state. This instead refers to the state of the sea much like a weather forecast.

The Philippines, though a maritime country, does not use this concept. At least not in weather forecasting. But events of the last few days and during the first days of January points to the need of using this concept. Repeated suspension of ferry sailing and floodings have been frequent recently [see: “Wicked Weather Count: 2,500 Stranded in Bicol, 50 Homes Destroyed in Cebu, 16,000 Flood Evacuees in Agusan del Sur”, 1/15/09]

Let’s face it. Small ships and fishing vessels sink even without a storm warning, like now. It is because seas can be too rough if the monsoons are in full swing. Like now. But there is a crucial lack of forecasting the state of the seas or sea state.

A sea state refers to the height, period (the two components of a wave in physics) and character of waves of a large body of water (waves can be said to be confused which makes it more dangerous). The strength of the wind is just one factor in creating a sea state. The monsoon swell is another. And tides play a factor, too.

PAGASA, out local forecaster uses the term sea condition. It bases its reading on the old Beaufort wind scale but with 9 gradings (The modern Beaufort wind scale has 12 gradings with the additional grades 13-16 to describe strong tropical cyclones; but some countries even use the 17th grade to describe phenomenal wind forces).

The beauty of an integrated Beaufort scale is that it not only describe wind strength but also the sea conditions including wave height. This is the failing of tropical depression/typhoon forecast we use locally that has only 4 grades and is just the measure of the wind strength, basically.

One small advancement, at least, of PAGASA is that they now use the concept of a gale which is a very strong wind. A full gale, at 63-87kph generally describes our Typhoon Signal #1. So sometimes when PAGASA forecasts gale it is actually describing near-gale winds (not now because half of Philippine seas are under gale conditions and that is why there are waves that are in the range of 3.7-7.0 meters which is more than enough to cancel the trips of regional ferries [not the inter-island ferries from Manila]).

However, more advanced countries than us have sea state forecasts aside from tropical cyclone warnings. Rather than relying on transmissions from passing ships and coast watchtowers it now uses satellite imagery. Shouldn’t we be subscribing to these services? If the government can hardly procure Doppler weather radars there is no way we can launch a dedicated weather satellite.

The World Meteorological Organization (WMO), a specialized agency of the United Nations has a sea state code. Other countries have their own systems. Even NATO (North Atlantic Treaty Organization) has their “Definition of Sea States” and this one even has modal periods (period between waves). I have seen sea state definitions that even traces different causal conditions which is one reason for the dangerous conditions called confused waves (conflicting waves). With an understanding of the theory of modal periods collosal (or rogue) waves, which capsize boats and launches, can be anticipated.

It seems we are a little bit behind the times.

[Note: Images above describe a full gale or Force 8 on the Beaufort scale]

[Images credit: brianlean, lavoieverte]

Two Boat Sinkings, A New Year Ferry Suspension in Bicol, Wave Height and Gale

January 3, 2009


For thousands of Bicol ferry passengers the forlorn walls of the ferry terminals in Tabaco (Albay), Pilar and Matnog (both in Sorsogon) was their New Year’s eve sight. This came about because government authorities, on the advice of the weather bureau, suspended small crafts from sailing citing forecasts of waves of up to four meters high.

This suspension is probably a reaction to the recent sinking of the motor boat MB Mae Jan which plies the Calayan island to Aparri, Cagayan route in which about half of its 100 passengers died. It was said that the weather was fine when the boat left Calayan but it turned bad before the boat reached its destination. The incident highlighted the disregard of PAGASA (the Philippines weather forecasting bureau) advisories which warned of big waves for that day.

Maybe the suspension is only correct. Forecast of wave heights should be the governing factor in ferry trip suspensions rather than wind speeds which is the basis for typhoon forecasts. It is waves that primarily swamp and capsize ships and not the winds per se. People should probably start to understand now that ships can meet sinking incidents even without a typhoon warning (and I am glad PAGASA now uses the term ‘gale’ to describe stormy sea conditions). I hope that government will stress more the importance of heeding wave height forecasts and educate people accordingly.

Sometimes I wonder if we need MB Mae Jan incidents for us to learn these things. But with the new system I hope the lives lost in that incident and in the MB Don Dexter Cathlyn sinking off Dimasalang, Masbate which killed about 40 people would not have been in vain.

This day, this change had a new twist. Ferry trips in Bicol were again suspended but this time the reason for the suspension is the refusal of the ship captains to venture out to sea combined with the barring of sea travel by the the Coast Guard. I hope this development augurs a new era of more pro-active observance of sea safety. I think we have needlessly lost enough lives in sea tragedies over the years because of the bahala na (leaving things to providence) attitude.

However, I hope this will not augur a new era of over-cautious sailing when ships are grounded when a storm is still far away and it so happened only that there is already a typhoon warning. Economic oppurtunies are lost this way. There is no need to automatically suspend ships when it is still shining and wave forecast is still moderate.

For prudence, maybe a finer distinction between small ships is needed. Old sea travellers know that outriggers and motor boats which are wooden are more vulnerable than steel ferries and there are bigger ferries that can handle waves better. The should not all be lumped under the category of ‘small sea craft’.

More passengers will be stranded in the future, for sure. But maybe it will also teach them how to read weather forecasts especially those that are available on the Net which is numerous enough and is up-to-date.

[photo credit: freewebs]