Glossary

Tropical Wave - A disturbance embedded in the Easterly Trade winds. Tropical Waves propagate across the Atlantic between 10-23 mph and are associated with cloudiness, showers and thunderstorms. On average, between 60 - 70 Tropical Waves form yearly over the Atlantic.

Tropical Depression - A Tropical Cyclone with maximum sustained winds of 33 knots (38 mph) or less.

Tropical Storm - A Tropical Cyclone with maximum sustained winds ranging from 34 to 63 knots (39 to 73 mph). At this stage it becomes a "names" system. E.g. Tropical Storm Tomas.

Hurricane - A Tropical Cyclone in which maximum sustained winds are 64 knots (74 mph) or more.

Saffir-Simpson Hurricane Wind Scale:

The Saffir-Simpson Hurricane Wind Scale is a 1 to 5 categorization based on the hurricane's intensity at the indicated time. The scale provides examples of the type of damage and impacts associated with winds of the indicated intensity. The following table shows the scale broken down by winds:

Category Wind Speed (mph) Damage
1 74 - 95 Very dangerous winds will produce some damage
2 96 - 110 Extremely dangerous winds will cause extensive damage
3 111 - 129 Devastating damage will occur
4 130 - 156 Catastrophic damage will occur
5 > 156 Catastrophic damage will occur


Tropical Storm Warning - An announcement that sustained winds of 34 to 63 knots (39 to 73 mph) are expected somewhere within the specified area within 36 hours.

Tropical Storm Watch - An announcement that sustained winds of 34 to 63 knots (39 to 73 mph) are possible within the specified area within 48 hours.

Hurricane Warning - An announcement that sustained winds of 64 knots (74 mph) or higher are expected within a specified area. The warning is issued 36 hours in advance of the anticipated hurricane. 

Hurricane Watch - An announcement that sustained winds of  64 knots (74 mph) or higher are possible within a specified area. The hurricane watch is issued 48 hours in advance of the anticipated hurricane.

Showers - Precipitation relatively short-lived but may last for up to an hour.

Isolated Showers - Showers generally covering less than 25% of the forecast area.

Widely scattered Showers - Showers generally covering 25% to 40% of the forecast area.

Scattered Showers - Shower generally covering 40% to 60% of the forecast area.

Widespread Showers - Showers generally covering more that 60% of the forecast area.

Fair - Cloud cover of 1 or 2 oktas of low and/or mid-level clouds during the forecast period. NB Okta is a unit used in meteorology to measure cloud cover. It is measured in eighths. Therefore, 1 okta is equivalent to 1/8.

Partly Cloudy - Cloud cover of 3 or 4 oktas of low and/or mid-level clouds during the forecast period.

Cloudy - Cloud cover of 5, 6 or 7 oktas of low and/or mid-level clouds during the forecast period.

Overcast - Cloud cover of 8 oktas (the entire sky) of low and/or mid-level clouds during the forecast period.