one kilometer (km):

0.62 mile

0.54 nautical mile

one mile (m):

1.61 kilometer

0.87 nautical mile

one nautical mile (nm):

1/60 degree latitude

1.85 kilometer

1.15 mile

one knot (kt):

one nautical mile per hour

1.85 km per hour

1.15 mile per hour (mph)

Use the following table for a quick estimate of travel time of a tropical system to the Leeward islands.

Example: Suppose that the center of a tropical storm is located at 15° N, 40° W, moving at 18 mph.
Most easterly Leeward islands located at around 61° W. This is a distance of 61-40=21° longitude. At 15° N this equals to 21x66.8= 1403 miles. So it will take around 1403/18= 78 hours or a 3 days and 6 hours to reach the islands. This is a rough estimate because the center of the storm has to stay on the same latitude and keep travelling at the same speed. You can also use the above form to calculate the distance and ETA.

The Marine Advisories give information about the current and forecasted windfield and sea conditions around the center of the storm. Important to check is that if a Hurricane does not make landfall to see how close it passes by.

An example of a small piece taken out of the Marine Advisory of Hortense of 11PM/Sep 11:

     EYE DIAMETER  16 NM
     MAX SUSTAINED WINDS  85 KT WITH GUSTS TO 105 KT
     64 KT....... 50NE  25SE  25SW  25NW
     50 KT.......100NE  50SE  30SW  60NW
     34 KT.......175NE 150SE  50SW 120NW
     12 FT SEAS..175NE 150SE  50SW 120NW
     ALL QUADRANT RADII IN NAUTICAL MILES

Tropical disturbance, tropical wave:

Unorganized mass of thunderstorms, very little, if any, organized wind circulation.

Tropical depression:

Evidence of closed wind circulation around a center with sustained winds from 20-34 knots (23-39 mph).

Tropical storm:

Maximum sustained winds are from 35-64 knots (40-74 mph). The storm is named once it reaches tropical storm strength.

Hurricane:

Maximum sustained winds exceed 64 knots (74 mph).

Category One - A Minimal Hurricane

Winds: 74-95 mph, 64-83 kts, 119-153 km/h

Minimum surface pressure: higher than 980 mbar

Storm surge: 3-5 ft, 1.0-1.7 m

Damage primarily to shrubbery, trees, foliage, and unanchored homes. No real damage to other structures. Some damage to poorly constructed signs. Low-lying coastal roads inundated, minor pier damage, some small craft in exposed anchorage torn from moorings. Example: Hurricane Jerry (1989)

Category Two - A Moderate Hurricane

Winds: 96-110 mph, 84-96 kts, 154-177 km/h

Minimum surface pressure: 979-965 mbar

Storm surge: 6-8 ft, 1.8-2.6 m

Considerable damage to shrubbery and tree foliage; some trees blown down. Major damage to exposed mobile homes. Extensive damage to poorly constructed signs. Some damage to roofing materials of buildings; some window and door damage. No major damage to buildings. Coast roads and low-lying escape routes inland cut by rising water 2 to 4 hours before arrival of hurricane center. Considerable damage to piers. Marinas flooded. Small craft in unprotected anchorages torn from moorings. Evacuation of some shoreline residences and low-lying areas required. Example: Hurricane Bob (1991)

Category Three - An Extensive Hurricane

Winds: 111-130 mph, 97-113 kts, 178-209 km/h

Minimum surface pressure: 964-945 mbar

Storm surge: 9-12 ft, 2.7-3.8 m

Foliage torn from trees; large trees blown down. Practically all poorly constructed signs blown down. Some damage to roofing materials of buildings; some wind and door damage. Some structural damage to small buildings. Mobile homes destroyed. Serious flooding at coast and many smaller structures near coast destroyed; larger structures near coast damaged by battering waves and floating debris. Low-lying escape routes inland cut by rising water 3 to 5 hours before hurricane center arrives. Flat terrain 5 feet of less above sea level flooded inland 8 miles or more. Evacuation of lowlying residences within several blocks of shoreline possibly required. Example: Hurricane Gloria (1985)

Category Four - An Extreme Hurricane

Winds 131-155 mph, 114-135 kts, 210-249 km/h

Minimum surface pressure: 944-920 mbar

Storm surge: 13-18 ft, 3.9-5.6 m

Shrubs and trees blown down; all signs down. Extensive damage to roofing materials, windows and doors. Complete failures of roofs on many small residences. Complete destruction of mobile homes. Flat terrain 10 feet of less above sea level flooded inland as far as 6 miles. Major damage to lower floors of structures near shore due to flooding and battering by waves and floating debris. Low-lying escape routes inland cut by rising water 3 to 5 hours before hurricane center arrives. Major erosion of beaches. Massive evacuation of all residences within 500 yards of shore possibly required, and of singlestory residences within 2 miles of shore. Example: Hurricane Andrew (1992)

Category Five - A Catastrophic Hurricane

Winds: greater than 155 mph, 135 kts, 249 km/h

Minimum surface pressure: lower than 920 mbar

Storm surge: higher than 18 ft, 5.6 m

Shrubs and trees blown down; considerable damage to roofs of buildings; all signs down. Very severe and extensive damage to windows and doors. Complete failure of roofs on many residences and industrial buildings. Extensive shattering of glass in windows and doors. Some complete building failures. Small buildings overturned or blown away. Complete destruction of mobile homes. Major damage to lower floors of all structures less than 15 feet above sea level within 500 yards of shore. Low-lying escape routes inland cut by rising water 3 to 5 hours before hurricane center arrives. Massive evacuation of residential areas on low ground within 5 to 10 miles of shore possibly required. Example: Hurricane Camille (1969)