WEATHER EXERCISE NAME:

QUESTIONS ONE

Define the following:

(a) trade wind
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(b) pressure gradient
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(d) strong wind warning
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	Before	At the front	After
Wind direction and strength
Barometric Pressure
Temperature

2 Detail the typical weather associated with a cold front by completing the table.

3 Describe
(a) how an aneroid barometer works.

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(b) how to take a reading from an aneroid barometer.

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4 A Coxswain at sea in inshore coastal areas will have a range of sources of weather information available, some of which will be more reliable or more up to date than others.

5

List these sources in order of importance for reliability or currency, and justify your selection.
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List your actions upon hearing a cyclone warning for your area while at sea (include options for a major port or a haven in your vicinity).
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ANSWERS ONE

1 (a) Trade wind is the name given to the wind flowing around the pressure systems and between the highs and the lows.

(b) Pressure gradient is the change in atmospheric pressure over a distance. The steeper the pressure gradient the stronger the wind will slow from the high to the low. A steep pressure gradient is represented by isobars being close together on a weather map.

(c) Sea breeze is a daily pattern caused by difference in temperature between land and sea. As the land warms up through the day the air over the land rises and air flows onshore from over the sea to replace it. The sea breeze averages 15 to 18 knots.

(d) A strong wind warning is issued when winds are expected from 25 to 33 knots.

2. Weather associated with a cold front:

	Before	At the front	After
Wind direction and strength	Northerly backing to NW and increasing in strength as the front approaches.	Suddenly and sometimes violently backing into the SW. May be accompanied by a storm.	Settles into SW to SE and begins to drop off after 24 hours usually..
Barometric Pressure	Steady drop for 2-3 days prior to the front.	At its lowest. Begins to rise rapidly as the cold air pushes through.	Continues steady climb depending on pressure gradient.
Temperature	Warm	Sudden drop	Remaining cool to cold.

3 (a). An aneroid barometer has a pointer attached by a delicate mechanism to a partial vacuum chamber. As the atmospheric pressure changes the chamber expands and contracts, moving the mechanism and thereby moving the pointer.

(b). At each reading the ‘set hand’ is set to cover the pointer so that at the next reading the trend, whether rising or falling, can be seen and by how much. Before the reading is taken the glass should be tapped lightly to ‘free’ the mechanism, the reading taken and the ‘set hand’ reset. When looking for a trend, diurnal variation should be taken into account (lowest at 4.00 am and 4.00 pm and highest 10.00 am and 10.00 pm).

4. Sources of weather information at sea:

Scheduled coastal weather forecasts through Coast Stations on HF and VHF. This service, designed for mariners, gives the synoptic situation followed by a detailed regional forecast for your area for the next 12 hours and is followed by locality reports from a number of automatic and manned weather stations. It has a high degree of reliability as a forecast and warning should not be ignored.

Own observations serve to confirm the official forecast but are unreliable as a forecasting tool. They are, however, vitally important for immediate warning of developing severe local conditions which may not have been forecast.
On demand weather information through volunteer rescue groups on HF, VHF or 27 MHz. While this information will be the official Bureau of Meteorology forecast it will not be as detailed as the Coast Station report. Also, not many volunteer rescue groups are continuous operations.
Local commercial radio stations broadcasting boating weather information in conjunction with regular news services. Some of these services are reliable, quality transmissions and could be moved higher up the list.
The barometer is of limited value for forecasting. However, it will show trends and show when you have passed through a trough line. This can be vitally important with severe local depressions.

5. Actions on hearing a cyclone warning:

Prepare your vessel for heavy weather and make for the nearest cyclone anchorage.
If the haven is major port with a cyclone emergency plan, contact the Harbour Control on arrival on VHF and obtain advice about where you are to proceed and what preparations you need to make.
If the haven does not have a cyclone plan try to find a small creek within a mangrove forest and secure your vessel there.
Avoid anchoring in the lee of islands. If the cyclone passes over you, you may find yourself on a lee shore.
Also try to avoid anchoring amongst other boats. If one or more drag you may get taken as well.
Monitor radio broadcasts to keep up to date with the location and movement of the cyclone.

Practical Activities

1 With the assistance of your Master/facilitator estimate the wind speed in knots and describe the sea state.

2 Obtain a synoptic chart for the day, either from the newspaper or from the Bureau of Meteorology. From the information on the synoptic chart ascertain the day’s weather and write a report. Check the report that you have written with the forecast put out by the Bureau of Meteorology or in the newspaper.

3 From when you first wake up in the morning write down the wind speed and direction every two hours. Avoid the day’s forecast until the end of the day when you can compare your finding with forecast.

The above activities will assist in addressing the key competencies of analysing and organising information, using technology, communicating ideas and information and working with others.

QUESTIONS TWO

1 List the information that you would expect to receive in a marine weather forecast.

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2 Describe the indications of a TRS

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Describe the safety precautions that you should take on a small vessel in the vicinity of a TRS.

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ANSWERS TWO

1. Information given:

Time of issue

Forecast area

Expected wind direction and speed

Expected sea and swell condition

Visibility (if below 2 miles)

Any other significant weather

Any major changes expected during the forecast period

Warnings

Strong Wind Warning: winds expected over 25 knots:

Gale Warning: winds expected over 35 knots

Storm Warning: winds expected over 48 knots

Cyclone Warning: issued as appropriate, with information about the location and expected movement of the centre of the storm, as well as the likely wind strength

Information given:

Time of issue

Area affected

Wind direction and strength

Sea state

Outlook

2. a) Coast radio stations will be issuing frequent and regular warnings, including the best information available of the position of the centre and its expected movement.

A definite, unusually steep fall in the barometric pressure. If the corrected pressure is below more than 3 hPa below normal, beware! If it is more than 5 hPa below normal, there is probably a storm within 200 miles. When checking the barometer to see if it is below “normal”, it is essential to take into account the diurnal variation.

They are the two most significant indicators. The remaining warning signs are useful, but not conclusive on their own.

c) Appreciable change in the direction and strength of the wind.

d) Unusual clarity of the atmosphere, remarkable visibility.

e) Extensive high cirrus cloud, swirling in towards the storm centre, and reflecting lurid colouring at sunrise and sunset.

f) In the open sea, swell from the direction of the storm centre.

g) High Humidity and rain increasing as TRS approaches.

A prudent ship’s Master should be aware of his/her vessel’s sea vessel in adverse weather conditions and steps to take to prepare the vessel handling ability, knowledge of the vessel’s stability, how to handle the for heavy weather.

Check:

The anchor gear to see that the anchor is secured, the stopper fitted, winch brake on, spurling pipe and any other openings made watertight.

Heavy objects or cargo that could be safely stowed below decks should be shifted.

Deck cleared of any loose debris or equipment. All equipment on deck is made secure.

All watertight doors, hatch covers and openings to below deck secured and water tight.

Freeing ports and scuppers checked to see they are free and working and a deck life line rigged.

Bilges should be pumped, and any tanks, if possible, either emptied or pressed up to reduce loss of stability through “free surface” effect.

Engine, steering gear. Perform routine checks and maintenance.

Life saving and fire fighting appliances. Have flares, grab bag and lifejackets on hand.

Put position on chart and report to a shore station with a radio check.

Have a meal and prepare simple food for later.

Determine the particular area of the storm you are in:

If you are in the dangerous semicircle put the wind on the port bow and steam as fast as possible, hauling round with the wind.

If you are in the path of the storm, or in the navigable semicircle put the wind on the port quarter and steam as fast as possible, hauling round with the wind.

It is essential to keep a close eye on the storm's movement, since any individual storm may behave irrationally. They are highly unpredictable, and it is not sufficient to assume that any particular storm will obey the rules. If the storm changes course, then it may be necessary for you to alter your own course of action.