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Orals Chief Mates > Met and Synoptic Charts, TRS and Reporting > Flashcards

Met and Synoptic Charts, TRS and Reporting Flashcards

1
Q

Types of weather instruments on the Bridge and their uses?

A

Hygrometer

  • Measures the humidity of the air
  • Two thermometers (one wet, one dry) stored in a Stevenson screen on the bridge wing
  • Difference between the wet and dry bulb can be used to workout the dewpoint from the dewpoint able in the Mariners handbook.
  • When the dewpoint is within 5° of the sea surface temperature then fog can be expected

Barometer

  • Measures atmospheric pressure
  • Periodical readings can inform you of the trend
  • High pressure = calm, clear, sunny conditions but also possible trapped cloud or fog
  • Low pressure = Clouds and precipitation can be expected with areas of deep lows potentially leading to storms

Anonemeter
- Measures the wind speed and direction

Sea Surface Temperature

  • Sensor in the hull
  • Water intake temp sensor
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2
Q

What are the key relationships when describing weather on a synoptic chart?

A

1st Relationship
- Clouds = Rain = Reduced vis

2nd Relationship
- Pressure drop = closer isobars = wind = sea

These relationships can be used to describe the weather where two air masses meet (a weather front)

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3
Q

Describe the weather as you pass from a warm front through to a cold front?

A

Warm Front

  • Warm air rising over cold air
  • Warm air condenses forming an increasing amount of cloud, rain and reducing vis
  • Pressure drops, the wind picks up and sea state worsens
  • So, as you pass under a warm front the weather will deteriorate

Warm Sector

  • Pressure steady = steady wind
  • light rain or drizzle
  • Potential for fog and mist - if clouds have formed low enough
  • Overall, the weather will remain the same

Cold Front
- Cold air moving under a warm air
- Rising warm air = clouds = heavy rain (potential hail and thunder) = poor vis
- Pressure drop = squally wind = worsening sea state
Behind the Cold Front
- Just cold air = fewer clouds (to blue skies) = no rain = better vis
- No rising air = reducing wind strength = calmer seas

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4
Q

What the signs of an approaching TRS?

A
  • Possible TRS if the barometer is 3mb below mean for that area- found in sailing directions
  • Definite TRS if the barometer is 5mb below mean
  • Significant change in wind and strength and direction
  • Long low swell from the direction of the TRS
  • Squally heavy rainfall in the vicinity of TRS
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5
Q

What weather can be expected at an occluded front?

A
  • This is when the cold front has caught up with the warm front meaning the warm sector has gone. Both warm front weather and cold front weather would be experienced here
  • So, low heavy cloud continuous rain, moderate wind and sea, poorer vis. Immediately after the warm front passes you will get heavy squally showers associated with the cold front, wind backs then veers considerably, confused seas, very poor vis
  • Once this passes the weather will then start to improve
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6
Q

How clouds are named

A
  • Cirro or Cirru = high alitude
  • Cumulo = cauliflower shape
  • Stratu or strato = layered
  • Nimbu or nimbo = rain bearing
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7
Q

What type of clouds you get at the different fronts

A

Cirrus, Cirrusstratus, Cumulonimbus, Altocumulo = Cold front
Cirrus, Cirrostratus, Altostratus, Nimbostratus = warm front

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8
Q

What type of dangers messages must the Master send as per SOLAS Ch V Reg 31?

A
  • Dangerous Ice
  • Dangerous derelict
  • Other direct danger to Navigation
  • TRS
  • Sub-freezing air temps with gale force winds causing severe ice accretion
  • Winds above Force 10 with no previous storm warning received
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9
Q

Who should the Master address the danger message too?

A
  • Ships in the vicinity and competent authorities
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10
Q

What are the four categories of Maritime Safety Information?

A
  • Nav Warnings
  • Met Warnings / forecasts
  • Other urgent safety related information
  • SAR information
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11
Q

What is the Master’s obligation regarding the World Wide Navigation Warning Service (WWNWS) transmissions?

A
  • All transmissions relating to navigation warnings or matters concerning life at sea are brought to the Masters notice or the of the OOW at the time, IMMEDIATELY ON RECEIPT.
  • Monitoring of nav warnings prior to sailing and whilst on passage. All warnings logged and bought to the attention of the OOW.
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12
Q

What is the WWNWS?

A
  • Established by the IHO and IMO.
  • Global service for broadcasting navigational warnings.
  • To give the mariner early information on incidents that may be a danger to navigation.
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13
Q

What are the 4 types of warnings?

A
  • NAVAREA
  • Sub-area
  • Coastal
  • Local
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14
Q

What are the Main Features of NAVAREA Warnings?

A

Information vessels in main shipping lanes.
- New nav hazards
- Failures of important nav aids
- Information which may require changes to planned nav routes

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15
Q

What is the purpose of the International Safety Net Service?

A
  • Automatic broadcasting service of MSI.
  • MSI information is received via EGC directly to the ship.
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16
Q

What Information should be included in a danger message?

What additional information should you include of Ice accretion and Storms > force 10 not reported?

A
  • Type, of danger
  • Position, of observation
  • Time, of observation
  • Additional, ice accretion;
  • Air temp
  • Sea temp
  • Wind force and direction
  • Additional, Storms > force 10 not reported;
  • Pressure/ pressure trend
  • Wind direction/force
  • Vessel course and speed
17
Q

How is fog formed?

A
  • When air is cooled to its dew point it becomes saturated with water vapour and the condensation of this water vapour is what causes fog.
18
Q

What are the different types of fog?

A
  • Advection (Sea) Fog
  • Radiation Fog
  • Sea Smoke
19
Q

When does Advection fog occur?

A
  • When warm moist air flows over a cold sea.
  • Typical in areas where a warm and cold current meet (e.g. Labrador and Gulf Stream off New Found land)
20
Q

When does sea smoke occur?

A
  • Occurs in high lats when very cold air blow over a relatively warm sea.
  • The water vapour evaporating from the sea cannot be held by the very cold air so it condenses and forms fog.
21
Q

When does radiation fog occur?

A
  • Occurs over low lying land, on clear nights, typically.
  • The heat trapped in the earth cools and forms fog.
  • Can blow out onto the sea but never more then 10-15 miles
22
Q

What is a TRS?
Where do they form?
Typical movement and speed?

A

TRS = Tropical revolving storm (Typhoon, Cyclone, Hurricane)

  • A very low depression.
  • Form in warm water (≧26°C) of the tropics.
  • Start off around 10-15 knots in a WNW direction (N HEMP), WSW (S HEMP).
  • They may recurve around the STAC but movement can be erratic.
  • If a TRS does recurve then it usually slows down, possibly even stop, and then speed up again to 20-25 knots.
23
Q

What is the dangerous semi-circle and actions to take?

A
  • The dangerous half will always be in the direction that the TRS recurves
  • Put the wind on a bow and alter course to the same side as the wind backs/veers (N.hemp S+S / S.hemp P+P)
24
Q

Three reasons why the the advance quadrant of the dangerous semi-circle is the most dangerous?

A
  • Strongest winds.
  • Wind is pushing you towards centre of the storm.
  • TRS would recurve towards the vessel.
25
Q

What is the navigable semi-circle and actions to take?

A
  • Navigable semi-circle is opposite to the dangerous side. Storm would recurve away from the vessel
  • Put the wind on a quarter and alter course to the opposite side as wind backs (N.hemp STBD qtr + A/C port / S.hemp Port qtr + A/C stbd)
26
Q

How can determine the centre of the storm?

A

Apply Buy’s Ballots Law
- Face the wind, storm centre will lie 12 points to right in N.hemp and 12 points to the left in S.hemp.

27
Q

How can I determine if I am behind or in front of the trough line?

A
  • If pressure is decreasing you are in front
  • If pressure is increasing you are behind
28
Q

If I am in a TRS but the wind does not appear to be backing or veering, where am I and what action should I take?

A
  • You are in the path of the storm.
  • Take action as you would in a navigable semi-circle.
29
Q

Which way does the wind rotate in N.hemp and S.hemp?

A

N.hemp
- Anti-cyclone - clockwise
- Cyclone - anti-clockwise

S.hemp
- Anti-cyclone - anti-clockwise
- Cyclone - clockwise

30
Q

Why do TRS not form in the South Atlantic

A
  • Water temp is not warm enough, cold water is brought up from the South Pole by the Benquella current
  • There is a high amount of wind shear in the atmosphere which stops a TRS from forming is vertical column of circulating air therefore stops it from forming

Orals Chief Mates (33 decks)

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