This document provides information on tropical cyclones, including their development, stages, characteristics, forecasting, and mitigation strategies. It defines a tropical cyclone and describes the environmental conditions needed for development. The stages of development from tropical wave to hurricane are explained. Characteristics like cloud formations, pressure patterns, and wind distributions are outlined. Forecasting methods and challenges are touched on, including improving forecast accuracy over time. Finally, strategies for mariners to monitor storms and evade tropical cyclones at sea or in port are presented.

2. * These are just of few of the references available
covering Tropical Cyclones, their effects on the
Marine Industry and Marine Safety. *
Mariner’s Guide for Hurricane Awareness in the North Atlantic
Basin (NOAA)
American Practical Navigator (Bowditch)
Port Heavy Weather Guide
Hurricane Havens Handbook for the North Atlantic (U.S. Navy)
REFERENCES

3. TROPICAL CYCLONE
DEFINED!
A warm core, non-frontal,
synoptic scale system with
cyclonically rotating winds
characterized by a rapid
decrease in pressure and
increase in winds toward the
center of the storm.
Cyclones develop over
tropical or subtropical
waters and have a definite
organized circulation.

4. How do they develop?
Favorable environmental conditions that must be
in place before a tropical cyclone can form:
– Warm ocean waters (at least 80°F / 27°C).
– An atmosphere which cools fast with height (potentially
unstable).
– Moist air near the mid-level of the
troposphere (16,000 ft / 4,900 m).
– Generally a minimum distance of at least 300
miles (480 km) from the equator.
– A pre-existing near-surface disturbance.
– Little vertical wind shear between the surface and
the upper troposphere. (Vertical wind shear is the change
in wind speed with height.)
– Outflow aloft/exhaust

5. STAGES OF
DEVELOPMENT
Tropical Depression(TD): A tropical cyclone with wind speeds up to 33
knots. Identified by the letters “TD” and suffixed by a number (TD-01:
the first tropical depression of the current calendar year.....TD-02, the
second, etc...)
Tropical Storm (TS): A tropical cyclone with wind speeds 34 to 63
knots. Identified by names in alphabetical order consistent with formation
date/time. (TS Arthur, Bertha...).
Hurricane: A tropical cyclone with wind speeds greater than 63 knots.
Identified by the same name it had as a TS.

6. TROPICAL (EASTERLY) WAVE
No significant winds or seas
No defined near surface
circulation
Identified by areas of
Convergence (thunderstorms)

7. TROPICAL DEPRESSION
(Formative Stage)
Winds < 34 kts
Tropical wave develops a
weak cyclonic circulation
Identified by thickening
clusters of thunderstorms
on satellite
Central pressure falls
rapidly below 1002mb if
system intensifies

8. TROPICAL STORM
(Immature to Mature Stage)
Winds 34 - 63 kts
Closed formation expands with spiral
bands becoming better organized
Increasing sea state makes navigation
near the center increasingly
difficult and dangerous

9. HURRICANE / TYPHOON / WILLY-WILLY
(Mature Stage)
Winds > 63 kts
DANGEROUSLY HIGH
SEAS navigation severely impaired
Radius of strong winds may exceed 350
NM
Gale Force Winds extend out further in
right front quadrant (typically 120 NM)

10. TROPICAL CYCLONE
Stages of Development
1. Tropical Easterly Wave 3. Tropical Storm
2. Tropical Depression 4. Hurricane

11. Most damaging aspects of
a hurricane:
AT SEA:
HIGH SEAS
HIGH WINDS
INPORT:
STORM SURGE
TORNADO/SVR TSTMS
HIGH WINDS

12. HURRICANE CATEGORIES
Category 1 (Minimal) - Winds 64 to 82 knots, storm surge 4 to 5 ft above
normal. No real damage to building Structures. Low lying coastal areas
flooded, minor damage to piers. Examples Irene 1999 and Allison 1995
Category 2 (Moderate) - Winds 83 to 95 knots, storm surge 6 to 8 ft above
normal. Minor damage to structures, poorly constructed buildings major
damage. Coastal and low lying escape routes flooded over, considerable pier
damage. Examples: Bonnie 1998, Georges (FL & LA) 1998 and Gloria 1985
Category 3 (Extensive) - Winds 96 to 112 knots, storm surge 9 to 12 ft above
normal. Major damage to structures, poorly constructed building destroyed.
Serious flooding along the coast, extensive flooding may extend inland 8
miles. Examples: Keith 2000, Fran 1996, Opal 1995, Alicia 1983 and Betsy
1965
Saffir- Simpson Scale

13. HURRICANE CATEGORIES
cont.
Category 4 (Extreme)
Winds 113 to 136 knots, storm
surge 13 to 18 ft above normal.
Extensive roofing and window
damage, complete destruction of
mobile homes. Areas above 10 ft
flooded inland up to 6 miles, major
erosion of beaches, massive
evacuation of coastal areas.
(ANDREW 1992)

14. HURRICANE ANDREW DAMAGE MAP

15. Category 5 (Catastrophic)
Winds above 137 knots, storm
surge greater than 18ft above
normal. Complete failure of roof
structures and very severe window
and door damage, some complete
buildings fail. Major damage to
structures lower than 15 ft above
sea level, massive evacuations of
residential units within 10 miles of
the coast.
(CAMILLE 1969)
AUG 16, 1969
HURRICANE CATEGORIES
cont.

16. Richelieu Apartments
The Power of a Category 5
“Hurricane Camille”
The Mansion
BEFORE!
AFTER!

17.  The map below shows where the seven basins noted for TC development
are located and typical tracks for each. It also has the average number of
tropical storms, and hurricanes, created in each basin.
TROPICAL CYCLONE
FORMATION,
LOCATION

18. Hurricane Season Atlantic
01 June - 30 November
Eastern Pacific
15 May - 30 November
Western Pacific
Year round
TROPICAL CYCLONE
FORMATION CONT.
2005 ATLANTIC
TROPICAL CYCLONE
NAMES
Lee
Maria
Nate
Ophelia
Philippe
Rita
Stan
Tammy
Vince
Wilma
Arlene
Bret
Cindy
Dennis
Emily
Franklin
Gert
Harvey
Irene
Jose
Katrina

20. Distribution of Surface Winds
Hurricane Andrew Strong CAT 4
 Winds are very light in
the eye, and increase
rapidly in the eyewall.
 Fastest winds are found
in the eyewall.
 Gale-force winds can
extend 250-400nm from the
center of the storm.

21. TROPICAL CYCLONE
CHARACTERISTICS
Feeder Bands (curved
lines of convection)
spiral inward to the Eye
Wall. Some of the most
violent weather
(tornadoes/severe
thunderstorms) occur in
these areas
“Pumping Action”
announces the
approach of, and
passing of the Tropical
Cyclone

22. Clouds
 Most significant clouds are
heavy Cumulus and
Cumulonimbus
 Spiral bands of CU/CB
inward toward outer edge of
eye
 Cirrus changing to
Cirrostratus and lowering,
good indicator of approaching
TC for the mariner
 Cloud sequence similar to
approaching warm front
TROPICAL CYCLONE
CHARACTERISTICS, CLOUDS

23. 18AUG 15Z 19AUG 12Z 20AUG 12Z
970
975
990
985
980
995
1005
1000
1020
1015
1010
18Z 15Z
21Z 00Z 03Z 00Z 03Z
06Z 06Z
09Z 15Z 18Z 21Z 09Z
Isobars nearly symmetrical or elliptical
in shape
Tightest isobaric gradient to right of
storms line of movement
Central pressures well below average
(890 – 940 mb not uncommon)
Barograph trace often shows “V” as
eye passes (not something a ship
wishes to see).
BAROGRAPH TRACE
Hurricane Bob 1991 Newport, RI
TROPICAL CYCLONE
CHARACTERISTICS, ISOBARS/PRESSURE

24. Time (UTC) Task / Event
00:00
Synoptic time, cycle begins, receive
aircraft fix (generally within +/- 00:30)
00:45
Receive satellite fix data (TAFB, SAB,
AFWA)
01:00 Initialize models
01:20
Receive model guidance, begin preparing
forecast
02:00
NWS/DOD hotline coordination call
(international coordination, if necessary)
03:00 Advisory package deadline
03:15 FEMA conference call
06:00 Next cycle begins
TPC/NHC Six-hour forecast cycle

25. Hurricane Isabel Track Guidance
1800 UTC 10 Sep 2003

27. NOT-SO EXCELLENT! “HURRICANE
KATE”
29 SEP 2003

28. 0
100
200
300
400
500
600
700
1954
1957
1960
1963
1966
1969
1972
1975
1978
1981
1984
1987
1990
1993
1996
1999
2002
year
error
in
n.
mi.
Tropical Prediction Center Performance Measures
yearly-average official track forecast errors and trend lines, Atlantic basin
120-hour
96-hour
72-hour
48-hour
24-hour
BIG IMPROVEMENTS IN TC TRACK FORECASTS OVER RECENT DECADE,
ESPECIALLY BEYOND 2 DAYS

29. UNDERWAY
 A wise mariner needs to know what to
do if warnings are in error (or plotted
incorrectly), or they get caught unaware,
and end up in the vicinity of a tropical
cyclone at sea!

30. MONITOR THE STORM
National Hurricane Center issues warnings every 6
hours 0300Z, 0900Z, 1500Z, 2100Z
NAVTEX
SafetyNet
Annotated on weather facsimile charts
Private weather routing companies
E-mail List servers from the National Hurricane Center

31. 1-2-3 Rule

32. WARNING’S
Upon Receipt of Warning:
1. Plot the current and forecast 24 hour storm positions and forecast radius of
35 kt winds.
2. Using a compass extend the radius of the forecast 24 hour 35 kt wind area
by 100 NM.
24 HR FORECAST POSITION CURRENT POSITION

33. WARNING’S, cont.
3. Draw tangents relative to the direction of the storm from the 35
kt radius (current position) to the outermost radius at the 24 hr
forecast position. Avoid the DANGER AREA
24 HR FORECAST POSITION CURRENT POSITION
DANGER
AREA

34. 4. Use the same procedure for the 48 and 72 hr forecast
positions, however, use 200 and 300 NM radii/respectively.
Avoid the DANGER AREA.
Current
24 Hr
48 Hr
72 Hr
200 NM
200 NM
300 NM
300 NM
DANGER
AREA
DANGER
AREA
DANGER
AREA
WARNING’S, cont.

35. Meteorological elements are
not uniformly distributed
throughout a tropical
Storm is divided into
left/right semicircles and
quadrants, relative to the
direction of motion
Usually strongest winds are
on right side in N.H. (added
to motion)
TROPICAL CYCLONE
EVASION

36. TROPICAL CYCLONE
EVASION cont.
Storm’s location relative
to own ship’s position:
Dangerous semi-circle:
Wind greater due to wind
augmented by the forward
motion of the storm.
“Less Dangerous” semi-circle:
Wind decreased by forward
motion of the storm.
Winds and seas force
vessel into path of storm.
Winds blow vessel away
from storm track.

37. TROPICAL CYCLONE EVASION
cont.
Ship in the “Dangerous” (right) semi-circle:
1. Maneuver ship so relative wind is from 045 degrees to starboard.
2. Continually hold course with respect to relative wind, making best way possible.
045 DEG REL

38. TROPICAL CYCLONE EVASION
cont.
Ship in the “Less Dangerous” (left) semi-circle:
1. Maneuver ship so that relative wind is from 135 degrees to starboard.
2. Hold course with respect to relative wind, and make best SOA.
135 DEG REL

39. AHEAD OF CENTER (ON STORM TRACK)
Maneuver ship so that relative wind is 157
degrees relative, hold course and speed.
157 DEG REL
BEHIND CENTER (ON STORM TRACK)
Avoid center by best practical course (storm
may recurve).
TROPICAL CYCLONE
EVASION cont.

40. DO NOT CROSS THE “T” unless the ship is > 300 NM ahead of the
storm and crossing right to left.
300 NM +
TROPICAL CYCLONE
EVASION cont.

41. Never cross the “T”: Do not plan to cross the track of a
hurricane.
NEVER LEFT TO RIGHT! Respect the negative effects that
heavy weather places on vessel speed/handling. Sudden
accelerations in hurricane motion can ultimately place a vessel in
conditions not originally expected, resulting in disaster!
Adjustments to course & speed in order to remain clear of the
danger area in a hurricane are the most prudent navigation
decisions a mariner can make in these instances.
If it becomes necessary to cross the “T” right to left, ensure you
are at least 300NM from the center.
Follow the 1 – 2 – 3 Rule
TROPICAL CYCLONE
EVASION cont.

42. Monitor warnings and advisories to prevent an encounter.
Forecast Track Tendencies: Comparison of the most recent NHC forecast track with
forecast tracks from the past 24 hours can be useful for determining a trend in the forecast
motion of a hurricane.
For instance, a comparison of forecast tracks issued every 6 hours over the last 24 hours,
may show a noticeable shift right or left (with respect to storm motion) in the forecast track
of a hurricane. This information may provide some indication as to how the forecast &
actual hurricane track are trending and provide more guidance in navigation planning for
avoidance, particularly in the 2-3 day forecast range & beyond.
TROPICAL CYCLONE
EVASION cont.

43. Assess your options: Plan Ahead. Never leave yourself with only a
single navigation option when attempting to avoid a hurricane.
Sea room to maneuver is not a significant factor when operating in the
open waters of the North Atlantic, but becomes extremely important in the
confined waters of the Western Caribbean Sea/Gulf of Mexico.
More often than not, early decisions to leave restricted maneuver areas
are the most sensible choice.
TROPICAL CYCLONE
EVASION cont.

45. IN PORT

46. MONITORING THE STORM
NHC Warnings/Bulletins
Local Radio / TV stations
Port Authority / Coast Guard
Internet

47. CONDITIONS OF READINESS
CONDITION 5 - Destructive force winds (35 kts or as specified ) are possible
within 96 hours.
CONDITION 4 - Destructive force winds are possible within 72 hours.
Whiskey
CONDITION 3 - Destructive force winds are possible within 48 hours.
X-Ray
CONDITION 2 - Destructive force winds are anticipated within 24 hours.
Yankee
CONDITION 1 - Destructive force winds are anticipated within 12 hours.
Zulu
These are the most common conditions of readiness.

48. Stay Inport
or
Ride it out at Sea?
Factors to consider!
The decision to leave port for hurricane avoidance must be made very
early, and must be balanced with a number of other factors
- Storm Intensity, Size, Strength, and Speed.
- Port Facilities, Berthing & Shelter Requirements
- 24 hours prior to onset of gale force winds.
- Probability of Hit (angle of approach)
- Vessel, size, speed, engineering status
- Time window to clear last vessel
- Vessel Route (safe, heavy seas, etc...)
* Early decisions to leave port in an attempt to avoid hurricanes are crucial.*

49. 1
1
6
2
3
4
5
7
8
21
19
20
12
11
9
10
14
13
17
16
18
15
1 - BOSTON
2 - NEWPORT
3 - NEW LONDON
4 - NEW YORK CITY
5 - PHILADELPHIA
6 - NORFOLK
7 - MOREHEAD CITY
8 - CHARLESTON
9 - SAVANNAH
10 - KINGS BAY
11 - MAYPORT
12 - PORT EVERGLADES
13 - KEY WEST
14 - TAMPA
15 - PENSACOLA
16 - GULFPORT
17 - NEW ORLEANS
18 - PORT ARTHUR
19 - GUANTANAMO BAY
20 - ROOSEVELT ROADS
21 - BERMUDA
Ports Evaluated in Hurricane Havens Handbook
for the North Atlantic (U.S. Navy)

50. TROPICAL CYCLONE
DISSIPATION
Recurvature:
Tropical storm curves towards the NNE-E.
Usually accelerating and decreasing in
strength, often increasing in size. Speed is
difficult to forecast.
Frictional forces of land:
Often becoming extra-tropical as storm
merges with frontal zone.
Unfavorable atmospheric/oceanographic
influences:
Includes, but not limited to, upper level
shearing, dry air intrusion in mid levels,
cooler sea surface temperatures, upwelling
behind other tropical systems, etc…
“Floyd”
“Charley”