Hurricane season is upon us, and it portends to be an active one.  With so many sources of information available, it’s easy to get overloaded by the variety of data and media hype. Here are some definitions and tips to weed out the key information and keep you prepared.

Definitions – adapted from National Hurricane Center’s Glossary:

Tropical cyclone – a rotating, organized system of clouds and thunderstorms that originates over tropical or subtropical waters and has a closed low-level circulation. TC’s rotate counterclockwise in the Northern Hemisphere. They are further classified as:

• Tropical Depression:  maximum sustained surface wind speed of 33 knots or less.
• Tropical Storm:  max sustained winds of 34 to 63 knots. Tropical Storms are assigned names.
• Hurricane: max sustained winds 64 knots or higher. In the western North Pacific, hurricanes are called typhoons; similar storms in the Indian Ocean and South Pacific Ocean are called cyclones.
• Major Hurricane: A tropical cyclone with maximum sustained winds of 96 knots or higher, corresponding to a Category 3, 4 or 5 on the Saffir-Simpson Hurricane Wind Scale.

Storm Surge – An abnormal rise in sea level accompanying a hurricane or other intense storm. (Storm surge is generally the most dangerous aspect of a storm for mariners in port, causing the greatest damage to life and property)

National Hurricane Center (NHC) is the primary source of hurricane forecasts for the US.  The information is distributed in various formats – text, graphic, voice – to reach all users.  Commercial organizations use the same base layer of information, but use value-added graphics and discussions. The combination can be confusing, so look carefully!

Weather Underground Graphic of Hurricane Irene, Aug 2011

Size Matters – a hurricane’s size is important because of the area it impacts, but its strength (intensity of wind speed) and track are even more important.  Things to look for in the graphics:

• Forecast track – most probable track of the storm’s center, based on models and meteorologists assessment.  
• Radius of possible storm center locations (measure of track uncertainty)
• Radius of damaging winds, where the strongest winds are nearest the storm center, and on the right leading quadrant (as the storm travels). 
• Wind Speed Probabilities – given for TS strength, 50 kt, and Hurricane strength, by geographic area.
• Storm Surge – depicted in feet above predicted astronomical tides along coastal regions.
• Mariner’s 1-2-3 Rule – refers to the rounded long-term NHC forecast errors of 100-200-300 nautical miles at 24-48-72 hours, respectively. It’s a graphical depiction the forecast uncertainty

Understanding these factors of a hurricane forecast will help you keep a sharp weather eye, so you can prepare appropriately.