Tropical Revolving Storms (TRS) - Detailed Notes

Tropical Revolving Storms (TRS)

Definition

• Intense tropical depressions that develop in tropical latitudes over large sea areas.
• Roughly circular atmospheric vortex originating in the tropics or subtropics.
• Winds of gale force (34 knots or Force 8) blow spirally inwards (anti-clockwise in the Northern Hemisphere, clockwise in the Southern Hemisphere).
• Violent winds and high, confused seas pose significant danger to ships, especially in restricted waters.

Naming Conventions

• WMO (World Meteorological Organization) maintains rotating lists of names for each Tropical Cyclone basin.
• Deadly or costly cyclones have their names retired and replaced.
• Short, distinctive names are used for quicker and less error-prone communication.
• Early naming was arbitrary (e.g., "Antje's hurricane").
• Mid-1900s: feminine names were used.
• Later, meteorologists used alphabetical lists.
• Male names started being used in the Southern Hemisphere before the end of the 1900s.
• Infamous storm names are retired at annual WMO Tropical Cyclone Committees meetings (e.g., Mangkhut, Irma, Maria, Haiyan, Sandy, Katrina, Mitch, Tracy).

Naming Procedure

• Strict procedure to determine cyclone names in an ocean basin.
• Tropical Cyclone Regional Body responsible determines the list at annual/biennial meetings.
• Five tropical cyclone regional bodies exist:
  • ESCAP/WMO Typhoon Committee
  • WMO/ESCAP Panel on Tropical Cyclones
  • RA I Tropical Cyclone Committee
  • RA IV Hurricane Committee
  • RA V Tropical Cyclone Committee
• Hurricane Committee determines a pre-designated list of hurricane names for six years at its annual session.
• Names are proposed by members, including National Meteorological and Hydrological Services.
• Tropical cyclones are not named after any particular person, nor with any alphabetical preference.
• Selected names are familiar to people in each region.
• The primary purpose is for easy understanding and remembrance to facilitate disaster risk awareness, preparedness, management, and reduction.

Structure of a Tropical Cyclone

Navigable Semicircle

• The side of a tropical cyclone to the left of its direction of movement in the Northern Hemisphere (to the right in the Southern Hemisphere).
• Winds are weaker, better for navigation.
• All parts of a TRS are dangerous to mariners.

Dangerous Semicircle

• The side of a tropical cyclone to the right of its direction of movement in the Northern Hemisphere (to the left in the Southern Hemisphere).
• Strongest winds and heavy seas.

1. The Eye or Vortex

• Calm central area of lowest pressure.
• Diameter between 4 and 30 miles, averaging about 10 miles.
• Roughly circular area of comparatively light winds and fair weather.
• Weather in the eye is normally calm, but the sea can be extremely violent.
• Little or no precipitation; sometimes blue sky or stars are visible.
• Region of lowest surface pressure than the surrounding environment.
• In severe cyclones, the eye usually looks like a circular hole in the central cloud mass.

2. The Eye-Wall

• Inner ring of hurricane-force winds.
• Width usually between 4 and 30 miles.
• Winds blow in a perfectly circular path with speeds up to 130 knots, with occasional gusts up to 150 knots.
• Very steep pressure gradient.
• Barograph registers a near-vertical trend (downward before the eye, upward behind it).
• Dense ring of cloud and tall thunderstorms produce heavy rains and the strongest winds (about force 6 or 7).
• Changes in the structure of the eye and eye wall can cause changes in wind speed.

3. The Outer Storm Area

• Area surrounding the eye-wall.
• Diameter between 50 and 800 miles, averaging about 500 miles.
• Winds are strong (about force 6 or 7), and the pressure gradient is much less than in the eye-wall.
• Angle of indraft of wind is about 45º, gradually decreasing to 0º in the eye wall.
• Cirrus cloud can be in the form of strands or filaments aligned and pointing towards the storm centre.
• Visibility is excellent, except in occasional showers.

Life Cycle of a Tropical Cyclone

• Complete life cycle spans about 9 days, but can range from 2-3 days to over 20 days.

Formation

• Dependent on six favorable environmental conditions available in the Inter Tropical Convergence Zone.
• Gains energy from latent heat, driven by thunderstorm activity and condensation of moist air.
• A gigantic vertical heat engine powered by earth’s gravity and rotation.

Premature Stage

• The area of convection continues and becomes more organized.
• Strengthening occurs simultaneously.
• Minimum surface pressure rapidly drops well below normal.
• Gale-force winds develop with the strengthening pressure gradient.
• The circulation centre is well defined, and an eye may begin to form.
• Satellite and radar observations show a distinctive spiral banding pattern.
• Devastating wind and storm surge effects upon coastline, but damage occurs usually within a small area.

Mature Stage

• If the ocean and atmosphere environment continue to be favorable, the cyclone may continue to intensify.
• This is the severe cyclone stage, where the cyclone is most dangerous.
• Approximately half of the cyclones reach this stage.
• Cyclonic circulation and extent of the gales increase markedly.
• In satellite images, cloud fields look highly organised and become more symmetrical with a well-centered, distinct round eye.
• This stage remains for a day or so at maximum intensity unless the cyclone remains in a highly favorable environment.

Decay Stage

• The warm core of TRS is destroyed.
• Central pressure increases, and maximum surface winds weaken.
• Decay may occur rapidly if the system moves into an unfavorable atmospheric or geographic environment.
• Heavy or medium rain can be available.

Factors Associated with the Decay of TRS

• Movement of these storms is controlled primarily by the movement of the upper warm core.
• They generally move westerly, then pole wards, then recurve easterly into higher latitudes.
• If they proceed over land, they lose intensity and degenerate into rain depressions.
• They may regenerate if they move over warm sea again.

Seasons of Greatest Frequency of TRS

• North Atlantic (south of Lat. $35^{\circ}N$): June to November; known as Hurricane.
• Eastern North Pacific: June through October; known as Hurricane.
• Western North Pacific: April through December, can occur in January to March; known as Typhoon (largest and strongest).
• North Indian Ocean (Bay of Bengal and Arabian Sea): February through October; known as Cyclone.
• South Indian Ocean (west of Longitude $100^{\circ}E$ and south of latitude $10^{\circ}S$): December through March; known as Cyclone.
• South Pacific and Australian Area (Longitude $105^{\circ}E$ to $160^{\circ}W$ between latitudes $50^{\circ}S$ and $20^{\circ}S$): December through April; known as Hurricane in the South Pacific and Willy-Willy in the Australian Area.
• Tropical revolving storms do not occur between latitudes $5^{\circ}N$ and $5^{\circ}S$ due to the very little effect of the Coriolis force and its absence at the equator.

WMO Nomenclature (Intensity)

• Tropical Disturbances: Low pressure area, maybe one closed isobar or none, no strong wind.
• Tropical Depression: Definite rotary circulation, one or more closed isobars, wind speed less than 34 knots.
• Tropical Storm or Severe Tropical Storm: Pressure lower than depressions, wind speed 34 to 63 knots.
• Hurricane/Typhoon/Cyclone: Pressure much lower, sustained winds 64 knots or over. Typhoons generally cover a larger area than hurricanes.

Recipe for a Cyclone

• Pre-heat the ocean to at least $26^{\circ}C$.
• Get an area of low pressure.
• Add lots of warm moist unstable and disturbed air.
• Mix well – using the Coriolis Force (between 5º-20ºNorth or South of the Equator).
• Cyclones need the Coriolis Force to generate spin; hence, they don’t form at the equator.

Cyclone Seasonality

• South Pacific: November to April (Southern Hemisphere summer), most frequent in January – March.
• Northeast Pacific: June to November.
• Northwest Pacific: All year round, most in early September, least in February & March.
• North Atlantic: June to November, most in August & September.
• North Indian basin: April to December, peaking in May and November.

Signs of an Approaching Cyclone

• A long low swell.
• Extensive high cirrus clouds in the direction from where the storm is approaching.
• A change of 3 hPa or more below the mean average pressure for the area.
• A marked change in the direction of wind and speed.
• Direction of storm: face the wind; the center lies approximately 90º on your left in the Southern Hemisphere, on your right in the Northern Hemisphere.

Hurricane Force Wind Definition

• Any wind averaging 64 knots.
• Storms are categorized based on wind speed.

Tropical Cyclone Warning Centers

• Located around the world with their own lists of names in alphabetical order.
• Two warning centers in the South Pacific (Brisbane and Fiji).
• Storms are named to make them easier to identify in weather reports.

Dissipation Factors

• Warm water is needed to sustain them; they dissipate over land or cooler waters.
• They are described as ‘pressure valves’ allowing the heat from the ocean to be released and dispersed.

Wind Patterns

• In the Southern Hemisphere, wind blows around the storm in a clockwise spiral flow inwards.
• General track is usually in a South Westerly direction but it may change and then head South East.

Formation Process

• Start as a cloud mass on one side of the equator and develop over warm seas (around 80 degrees Fahrenheit).
• Moisture and warm air rise, reducing atmospheric pressure, leading to a depression where moisture condenses to form large thunderclouds.
• Cold air rushes in to fill the void.
• As the Earth rotates, this air mass is bent and spirals upwards with great force, with swirling winds rotating with increasing speed forming a huge circle up to 2000 km across.
• The storm builds up and moves while being sustained by warm, moist air.

Main Causes

• Rising warm air from seas in equatorial regions is the main cause.
• This rising air condenses forming clouds while releasing massive amounts of heat.
• The combination of heat and moisture leads to the formation of many thunderstorms from which a tropical revolving storm can develop.

Impacts

• Extreme weather (high winds, thunder, lightning, torrential rain).
• Significant damage to infrastructure and loss of life.
• Flooding commonly occurs, especially when the storm crosses the coast.
• Low pressure and strong onshore winds produce a large increase in sea level, called a "storm surge."

Factors Affecting Hurricane Movement

• Hurricane movement is known as hurricane propagation.
• Hurricanes are steered by global winds.
• The environmental wind field guides a hurricane along its path.
• The hurricane propagates in the direction of this wind field, which also factors into the system’s propagation speed.

Trade Winds

• In the tropics, easterly winds steer a hurricane westward.
• In the Atlantic basin, storms are carried by these trade winds from the coast of Africa westward towards the Caribbean Sea and the North American coasts.

High and Low-Pressure Systems

• Large-scale high and low-pressure systems are embedded within the global winds.
• Clockwise rotation of air associated with high-pressure systems often causes hurricanes to curve northward.

Subtropical Ridge (Bermuda High/Azores High)

• Often dominates the North Atlantic Ocean.
• Atlantic hurricanes typically propagate around the periphery of the subtropical ridge.
• If the high is positioned to the east, hurricanes propagate northeastward into the open Atlantic Ocean without making landfall.
• If the high is positioned to the west and extends far enough to the south, storms are blocked from curving north and forced to continue west.

Beta Drift

• A hurricane drifts northwestward (in the Northern Hemisphere) due to beta drift.
• Arises because the strength of the Coriolis force increases with latitude for a given wind speed.
• Air moving northward on the east side of a hurricane acquires clockwise spin; air moving southward west of the storm acquires counterclockwise spin.

Mid-Latitudes

• As a hurricane propagates northward out of the tropics, the environmental wind field often becomes weak, causing the hurricane to slow down, stall, or move erratically.
• Once a hurricane reaches further north and enters the mid-latitudes, the environmental wind field usually becomes southwesterly or westerly.
• Causes the hurricane to recurve to the right and accelerate towards the north, northeast, or east.

Jet Stream

• If a hurricane encounters the jet stream, the storm may accelerate very quickly, allowing it to reach high latitudes, especially if it is travelling over a warm ocean current such as the Gulf Stream.

Vertical Wind Shear

• When vertical wind shear exists, the hurricane’s rotational wind field may tilt with height.
• The vertical wind shear may allow the lower circulation to push the upper one and the upper circulation to push the lower one, having a combined effect of changing the track of the entire hurricane.

Fujiwhara Effect

• If a hurricane is in close proximity to another similarly-sized atmospheric circulation, the two circulations may orbit cyclonically around a common point between them.
• This motion is known as the Fujiwhara effect.

Land Interaction

• Land interaction also may change the track of a hurricane, especially when the land is mountainous.
• Mountains can disrupt the center of a hurricane’s circulation, which may then reform on the other side of the mountains away from the trajectory of the hurricane’s track prior to crossing the mountains.

Hurricane Track Forecasting

• Hurricane movements can be very unpredictable, sometimes performing loops, hairpin turns, and sharp curves.
• Forecasters track hurricane movements and predict where the storms will travel as well as when and where they will reach land.

Factors that Contribute to the Intensity of a Revolving Storm

• Instability: Tropical revolving storms form close to the Inter Tropical Convergence Zone (ITCZ) where there is marked instability.
• Humidity: Storms mainly occur over the western parts of the tropical oceans where the air has had a long passage over the sea or where air has crossed over from the other hemisphere and has become saturated.
• Latitude: For a given pressure gradient the strength of the winds increases as the storm approaches the Equator.
• Temperature: Tropical revolving storms form over water surfaces with a water temperature of at least $27^{\circ}C$.

Hurricane Measurement

• Hurricanes are divided into five categories by wind speed using the Saffir-Simpson hurricane intensity scale.
• Destruction includes damage to permanent homes, widespread coastal flooding, uprooting of trees, toppling of power lines.
• Anticipation of such damages prompts evacuation of residents from the area of expected landfall.

Saffir-Simpson Hurricane Intensity Scale

Tropical Cyclone Track Forecasting

• Involves predicting where a tropical cyclone is going to track over the next five days, every 6 to 12 hours.

Factors Strengthening Tropical Cyclones

• Sea surface temperatures warmer than $79^{\circ}F$ ($26^{\circ}C$).
• Low vertical wind shear.
• Warm moist air.
• Ocean area along the projected storm track.

Factors Weakening Tropical Cyclones

• Cooler Sea surface temperatures less than $79^{\circ}F$ ($26^{\circ}C$).
• High vertical wind shear.
• Dry air.
• Land masses along the projected storm track.

Reasons for naming the dangerous Circle dangerous semicircle

• The side of a tropical cyclone to the right of the direction of movement of the storm in the Northern Hemisphere (to the left in the Southern Hemisphere), where the winds are stronger because the cyclone's translation speed and rotational wind field are additive.
• The opposite side is termed the navigable semicircle.
• the dangerous semicircle of the storm has the strongest winds and heaviest seas
• a sailing ship on this side tends to be carried into the path of the storm

Clouds and Precipitation

• Clouds forming over mountain tops due to wind moving upslope and converging.
• process for the cloud water, or ice, to grow large enough to fall as precipitation.
• A cloud is a visible aggregate of tiny water droplets and/or ice crystals suspended in the atmosphere and can exist in a variety of shapes and sizes. Some clouds are accompanied by precipitation; rain, snow, hail, sleet, even freezing rain.
• Introduction a number of cloud classifications, different types of precipitation, and the mechanisms responsible for producing them.

Characteristics

• Cause Warm ( over 27C) moist air rises from the surface of the sea.
• As it rises it meets cooler air and condenses to make clouds and rain.
• This condensation releases huge amounts of energy, producing strong winds.
• The winds are driven by the spin of the earth and go round and round.
• As the earth rotates the winds are sucked violently upwards in a vortex which can be 1,000km wide. Wind speeds can be as high as 200km per hour.
• These storms are fueled by damp air when they reach land, dry air is being sucked up and they loose energy.

Origin, Movement and Life Span

• Tropical revolving storms travel from place of origin in a westward direction and inclined more and more towards the pole and then curve eastward approximately in latitudes 20°N or S. The position where its westward movement changes to eastward is called the “point of recurvature”. Thus, in the northern hemisphere the general direction of movement is roughly west, northwest, north and finally northeast.
• In the southern hemisphere it is west, southwest, south and finally southeast. After reaching temperate latitudes the storms tend to dissipate (disperse) or join up with extra-tropical cyclones and lose its character as a tropical storm. The easterly wave gives the storm its initial westerly movement. However, some storms do not follow this pattern and move erratically.
• TRS originate in latitudes between 5° & 20° and travel between W and WNW in the NH and between W and WSW in the SH, at a speed of about 12 knots. Somewhere along their track, they curve away from the equator – curve to N and then recurve to NE in the NH; curve to S and then recurve to SE in the SH.

Terms Used in Connection with Tropical Revolving Storms:

• Storm Field – This is the region covered for the time being by the winds forming the storm.
• Track – The route over which a TRS is already passed.
• Path – The predicted route, over which, there is a possibility of the TRS passing at near future.
• Vertex or cod-which is the westernmost point, of the TRS, when recurving takes place.
• Vortex or Center or Eye – This is the central almost windless area within the ring of hurricane force wind, and where the atmospheric pressure (barometric pressure) is lowest. The sky above is usually clear but the sea is confused and mountainous. If the eye of the storm passes over the observer’s position, the winds suddenly weaken to just a breeze as the eye passes; the rain stops and the sky becomes clear that sunlight can be seen in the day, but confused and mountainous wave come from all sides, and the barometer reaches its lowest reading. When the eye has passed the wind resumes with full violence as suddenly as it stopped but from the opposite direction.
• Right- Hand Semicircle – This refers to right side half of the storm field for an observer looking towards the path. In the northern hemisphere this is the dangerous semicircle” and the forward quadrant is called the “dangerous quadrant.
• Left- Hand Semicircle – This refers to left side half of the storm field for an observer looking toward the path. In the northern hemisphere this is the“navigable semicircle.” In the southern hemisphere, the right- hand semicircle is the navigable semicircle, and the left- hand semicircle is the dangerous semicircle.
• Trough Line – This is the line through the center of the storm at right angles to the path. It is also the dividing line between falling (decreasing) and rising pressure.
• Bar of the Storm – This term means the advancing edge of the storm field.
• Angle of Indraft – This is the angle that the wind direction makes with isobars.

Typical Cloud Formations

• Cirrus, cirrostratus, altostratus, stratocumulus, cumulonimbus, and scuds.

Energy Source

• Latent heat released during condensation of water vapor in ascending tropical air mass currents.

Path

• The recurving is such that the storm travels around the oceanic high (which is situated at about 30°N and 30°S in the middle of large oceans).
• After recurving, the speed of travel increases to about 15 to 20 knots.
• Sometimes, a TRS does not curve or recurve at all but continues on its original path, crosses the coast, and dissipates quickly thereafter due to friction and lack of moisture.
• It is important to note that all TRSs do not follow such definite paths and speeds. In their initial stages, occasional storms have remained stationary or made small loops for as long as four days.

Determining the Semicircle

• First, determine the true wind direction.
• If the wind is veering (shifting to the right), the vessel is in the right-hand semicircle; if the wind is backing (shifting to the left), the vessel is in the left-hand semicircle.
• The rule is true in both hemispheres so that by means of this you will know whether your vessel is in the dangerous semicircle or in the navigable semicircle, the vessel is in the direct path of the storm, or is going at the same speed and direction as the storm.
• If you are not sure of the storm’s movement relative to the vessel, you should heave – to (stop the ship) until this is ascertained. The storm’s movement must be continuously checked either by radio weather reports or by means of actual observation as outlined in the above paragraphs.

Navigable and Dangerous Semicircles

• In the northern hemisphere (NH), conditions on the right-hand side of storms are more severe than those on their left-hand sides. For that reason, in NH, RHSC is called the “dangerous semicircle” and LHSC is called the “navigable semicircle”.

Signs of Approach

• Navigable semicircle — It is the side of a tropical cyclone, which lies to the left of the direction of movement of the storm in the Northern hemisphere (to the right in the Southern Hemisphere), where the winds are weaker and better for the navigation purpose, although all parts of TRS are more or less dangerous to mariners.
• Dangerous semicircle— It is the side of a tropical cyclone, which lies to the right of the direction of movement of the storm in the Northern Hemisphere (to the left in the Southern Hemisphere), where the storm has the strongest winds and heavy seas.

Warnings of Approach

1. Warning and alerting messages

• The Radio/Telex/NAVTEX and all other means at hand should be set on the right frequencies and monitored closely, for they broadcast comprehensive warnings with respect to known storms. Refer to the respective ALRS Volumes for more data and frequencies of radio stations in the vicinity. The Telex, although barely used, is also a very important tool that is high on accuracy.

2. Swell

• When there is no sight of intervening land, the sea might generate swell within a TRS, indicating an early warning of the formation of the same. Normally, the swell approaches from the direction of the storm.

3. Atmospheric Pressure

• Monitor the barometer closely in case you are suspicious of a brewing storm. If the corrected barometer reading falls below 3 mb or more for the mean reading for that time of the year (check the Sailing Directions for accurate information of pressure readings), you can expect a (Tropical Revolving Storm) TRS. Note that the barometer used must be corrected for latitude, height, temperature etc. to achieve maximum possible accuracy and efficiency.

4. Wind

• Wind direction and speed is generally fairly constant in the tropics. Variation from the normal direction for the area and season, and increasing wind speed, are indications of the approach of a Tropical Revolving Storm, i.e., an appreciable change in the direction or strength of the wind indicates a Tropical Revolving Storm (TRS) in vicinity.

5. Clouds

• A very candid and colorful sky at sunrise and sunset may be a sign of a brewing TRS. Presence of cirrus clouds is visible at a considerable distance of 300 to 600 miles from the TRS and as you approach the TRS, the clouds get lower and cover a bigger area (altostratus). Generally followed by cumulus clouds as you get closer to the Tropical Revolving Storm (TRS).

6. Visibility

• Although it might sound like an oxymoron, exceptionally good visibility exists when a TRS is lurking in proximity!

7. Radar

• The radar gives a fair warning of a Tropical Revolving Storm (TRS) about 100 miles prior to approaching the TRS. The eye may sometimes be seen on the screen. An area of rain surrounds the eye (the eye of the storm is the storm center) causing appreciable clutter on the radar screen Remember that though the signs might be visible on the radar, by the time it does become visible on the radar, the vessel is probably already experiencing high seas and gale force winds and rough weather overall. Action is to be taken before such a situation arises.

Development of a Category 2 Hurricane

*A general sequence of events that could occur during the development of a Category 2 hurricane (wind speed 96-110 mph) approaching a coastal area.

96 hours before landfall

• At first there aren’t any apparent signs of a storm. The barometer is steady, winds are light and variable, and fair-weather cumulus clouds appear.

72 hours

• Little has changed, except that the swell on the ocean surface has increased to about six feet and the waves come in every nine seconds. This means that the storm, far over the horizon, is approaching.

48 hours

• The sky is now clear of clouds, the barometer is steady, and the wind is almost calm.
• The swell is now about nine feet and coming in every eight seconds.

36 hours

• The first signs of the storm appear. The barometer is falling slightly, the wind is around 11 mph, and the ocean swell is about 13 feet and coming in seven seconds apart. On the horizon, a large mass of white cirrus clouds appear.
• As the veil of clouds approaches, it covers more of the horizon.
• A hurricane watch is issued, and areas with long evacuation times are given the order to begin.

30 hours

• The sky is covered by a high overcast. The barometer is falling at .1 millibar per hour; winds pick up to about 23 mph.
• The ocean swell, coming in five seconds apart, is beginning to be obscured by wind-driven waves, and small whitecaps begin to appear on the ocean surface.

24 hours

• Small low clouds appear overhead. The barometer is falling by .2 millibars per hour, the wind picks up to 34 mph. The wind driven waves are covered in whitecaps, and streaks of foam begin to ride over the surface. Evacuations should be completed and final preparations made by this time. A hurricane warning is issued, and people living in low lying areas and in mobile homes are ordered to evacuate.

18 hours

• The low clouds are thicker and bring driving rain squalls with gusty winds. The barometer is steadily falling at half a millibar per hour and the winds are whistling by at 46 mph. It is hard to stand against the wind.

12 hours

• The rain squalls are more frequent and the winds don’t diminish after they depart. The cloud ceiling is getting lower, and the barometer is falling at 1 millibar per hour. The wind is howling at hurricane force at 74 mph. The sea advances with every storm wave that crashes ashore, and foam patches.

6 hours

• The rain is constant and the 92 mph wind drives it horizontally. The barometer is falling 1.5 millibar per hour, and the storm surge has advanced above the high tide mark. Thesea surface a whitish mass of spray. It is impossible to stand upright outside without bracing yourself.

1 hour

• The rain becomes heavier. Low areas inland become flooded. The winds are at 104 mph, and the barometer is falling at 2 millibar per hour. The sea is white with foam and streaks. The storm surge has covered coastal roads and 16 foot waves crash into buildings near the shore.

After the Storm

1 hour after landfall

• The sky darkens and the winds and rain return just as heavy as they were before the eye. The storm surge begins a slow retreat, but waves continue to crash ashore. The barometer is rising at 2 millibar per hour, and the winds top out at 104 mph.

6 hours

• The flooding rains continue, but the winds have diminished to 92 mph. The storm surge is retreating and pulling inland debris out to sea.

12 hours

• The rain now comes in squalls, and the winds begin to diminish after each squall passes. The cloud ceiling is rising, as is the barometer at 1 millibar per hour. The wind is still howling at near hurricane force at 69 mph, and the ocean is covered with streaks and foam patches. The sea level returns to the high tide mark.

24 hours

• The clouds break into smaller fragments and the high overcast is seen again. The barometer is rising by .2 millibar per hour, the wind falls to 34 mph. The surge has fully retreated from land, but the ocean surface is still covered by small whitecaps and large waves.

36 hours

• The overcast has broken and the large mass of white cirrus clouds disappears over the horizon. The barometer is rising slightly, the winds are a steady 11 mph.

Actions in TRS, at port

• Double the moorings.
• Keep Engine standby.
• All persons to be onboard.
• Keep all LSA at the standby position.
• Rig lifeline at fore and aft.
• No slack tanks.
• All hatches should be securely battened down.
• All derricks should be lowered and secured.
• Adequate fenders should be placed between the ship and the jetty.

Actions in TRS, at anchorage

• If possible, first try to go to sea at safe distance with plenty sea room and sufficient depth of water or shift to a safe anchorage with enough shelter. Otherwise, do the following:
• Drop both anchors with several cables in water.
• Keep Engine standby.
• All persons to be onboard.
• Keep all LSA at the standby position.
• Rig lifeline at fore and aft.
• No slack tanks.
• All hatches should be securely battened down.
• All derricks should be lowered and secured.
• All bridge equipment (including Radar, fog-horn) and navigational lights (including emergency navigational lights) should be in standby mode.

Actions in TRS, At sea

If the vessel is in the dangerous quadrant:

• Proceed as fast as practicable with the wind 1 to 4 points on the stbd bow in NH (port bow in SH) – 1 point for slow vessels (less than 12 knots) and 4 points for fast vessels (more than 12 knots) altering course as the wind veers in NH (backs in SH).
• This action should be kept up until the pressure rises back to normal i.e. until the vessel is outside the outer storm area. If there is insufficient sea room, the vessel should heave to with the wind on the stbd bow (port bow in SH) until the storm passes over.

If the vessel is in the path of the storm or if in the navigable semi-circle:

• Proceed as fast as practicable with the wind about 4 points on the stbd quarter in NH (port quarter in SH), altering course as the wind backs in NH (veers in SH). This action should be kept up until the pressure rises back to normal i.e. until the vessel is outside the outer storm area.

Determining the approximate Bearing of approaching TRS

• To avoid the full fury of a tropical storm early determination of its location and direction of travel relative to the vessel’s position is essential. The Maritime Weather Broadcast (weather report broadcast by shore stations) provides information about the storm