Archive for the ‘rogue wave’ 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]