Atlantic Basin - The area including the entire North Atlantic Ocean, the Caribbean Sea, and the Gulf of Mexico.
El Niño - (EN) A 12-18 month period during which anomalously warm sea surface temperatures occur in the eastern half of the equatorial Pacific. Moderate or strong El Niño events occur irregularly, about once every 3-7 years or so on average.
Hurricane - (H) A tropical cyclone with sustained low level winds of 74 miles per hour (33 m s-1 or 64 knots) or greater.
Hurricane Day - (HD) A measure of hurricane activity, one unit of which occurs as four 6-hour periods during which a tropical cyclone is observed or estimated to have hurricane intensity winds.
Hurricane Destruction Potential - (HDP) A measure of a hurricane's potential for wind and storm surge destruction defined as the sum of the square of a hurricane's maximum wind speed (in 104 knots2)for each 6-hour period of its existence.
Intense Hurricane - (IH) A hurricane which reaches a sustained low level wind of at least 111 mph (96 kt or 50 m s-1) at some point in its lifetime. This constitutes a category 3 or higher on the Saffir/Simpson scale (also termed a ``major" hurricane).
Intense Hurricane Day - (IHD) Four 6-hour periods during which a hurricane has intensity of Saffir/Simpson category 3 or higher.
MATL - Sea surface temperature anomaly in the sub-tropical Atlantic between 30-50°N, 10-30°W
MPD - Maximum Potential Destruction - A measure of the net maximum destruction potential during the season compiled as the sum of the square of the maximum wind observed (in knots) for each named storm. Values expressed in 103kt.
Named Storm - (NS) A hurricane or a tropical storm.
Named Storm Day - (NSD) As in HD but for four 6-hour periods during which a tropical cyclone is observed (or is estimated) to have attained tropical storm intensity winds.
NATL - Sea surface temperature anomaly in the Atlantic between 50-60°N, 10-50°W
NTC - Net Tropical Cyclone Activity - Average seasonal percentage mean of NS, NSD, H, HD, IH, IHD. Gives overall indication of Atlantic basin seasonal hurricane activity (see Appendix B).
ONR - previous year October-November SLPA of subtropical Ridge in eastern Atlantic between 20-30°W.
QBO - Quasi-Biennial Oscillation - A stratospheric (16 to 35 km altitude) oscillation of equatorial east-west winds which vary with a period of about 26 to 30 months or roughly 2 years; typically blowing for 12-16 months from the east, then reverse and blowing 12-16 months from the west, then back to easterly again.
Saffir/Simpson (S-S) Category - A measurement scale ranging from 1 to 5 of hurricane wind and ocean surge intensity. One is a weak hurricane whereas 5 is the most intense hurricane.
SLPA - Sea Level Pressure Anomaly - The deviation of Caribbean and Gulf of Mexico sea level pressure from observed long term average conditions.
SOI - Southern Oscillation Index - A normalized measure of the surface pressure difference between Tahiti and Darwin.
SST(s) - Sea Surface Temperature(s).
SSTA(s) - Sea Surface Temperature(s) Anomalies.
Tropical Cyclone - (TC) A large-scale circular flow occurring within the tropics and subtropics which has its strongest winds at low levels; including hurricanes, tropical storms, and other weaker rotating vortices.
Tropical Storm - (TS) A tropical cyclone with maximum sustained winds between 39 (18 m s-1 or 34 knots) and 73 (32 ms-1 or 63 knots) miles per hour.
TATL - Sea surface temperature anomaly in Atlantic between 8-22°N, 10-50°W.
ZWA - Zonal Wind Anomaly - A measure of upper level ( ~ 200 mb) west to east wind strength. Positive anomaly values mean winds are stronger from the west or weaker from the east than normal.
1 knot = 1.15 miles per hour = .515 meters per second.