Low-pressure area—region of the atmosphere in which the pressures are lower than those of the surrounding region at the same level
Cyclone—a phenomenon in which winds spin inward in a counterclockwise direction in the northern hemisphere and in a clockwise direction in the southern hemisphere.
Tropical cyclone—when a cyclone is formed in the tropics; known as “bagyo” in the Philippines; classified (based on the strength of the winds) as supertyphoon, typhoon, storm and tropical depression
Supertyphoon—a tropical cyclone that has winds greater than 200 kilometers per hour
Typhoon—a tropical cyclone that has winds exceeding 118 kph
Storm—a tropical cyclone that packs winds of 64 to 118 kph
Tropical depression—a tropical cyclone with winds that do not exceed 63 kph
Hurricane—a tropical cyclone that occurs in the Atlantic Ocean and adjacent seas
Willy-willy—term that refers to a tropical cyclone that occurs in the eastern part of the Southern Indian Ocean
Storm Signal No. 4—the highest alert level for supertyphoons in the Philippines with very strong winds of more than 185 kph and may be expected in at least 12 hours; the area under this storm signal is very likely to be hit directly by the eye of the storm and damage can be very heavy.
In the United States, hurricanes with sustained wind speeds between 178 and 208 kph are classified as Category 3 under the Saffir-Simpson Hurricane Wind Scale used by the US National Hurricane Center while Category 4 hurricanes have winds between 209 and 251 kph. The strongest Category 5 hurricanes have wind speed of 252 kph and higher.
Intertropical convergence zone—a result of the northern hemisphere and southern hemisphere trade winds convergence
Thunderstorm—a weather disturbance that produces thunder and lightning aside from wind and rain
Tornado—a violently rotating column of air that reaches from the base of a cloud to the ground (in funnel shape) and made visible by condensation and debris; called a violent thundersquall in other areas
Philippine area of responsibility—refers to the designated area in the northwestern Pacific where the Philippine Atmospheric, Geophysical and Astronomical Services Administration is tasked with monitoring tropical cyclones; bounded by imaginary lines joining the following points: 25°N – 120°E, 25°N – 135°E, 5°N – 135°E, 5°N – 115°E, 15°N – 115°E and 21°N – 120°E
Habagat—local term for southwest monsoon; occurs when warm, moist air flows over the country from the southwest direction and characterized by heavy rainfall that may last for a week
Knot—a measure of speed equivalent to 1 nautical mile per hour used by the Joint Typhoon Warning Center, which is based in Hawaii.
Nautical mile—equivalent to 1.852 kilometers—Inquirer Research
Sources: Inquirer archives, websites of Pagasa, Severe Weather Information Center and National Weather Service Eastern Region Headquarters