Typhoon Kalmaegi has killed at least 114 people in the Philippines with even more missing and then hit Vietnam Friday. A second typhoon, Fong-Wong, is forecast to also hit the Philippines around Sunday and strengthen to a major storm by that time.

Facts about typhoons:

Hurricane? Cyclone? Typhoon? They’re all the same, officially tropical cyclones. But they just use distinctive terms for a storm in different parts of the world. Hurricane is used in the Atlantic, Caribbean Sea, central and northeast Pacific. They are typhoons in the northwest Pacific. In the Bay of Bengal and the Arabia Sea, they are called cyclones. Tropical cyclone is used in the southwest India Ocean; in the southwestern Pacific and southeastern India Ocean they are severe tropical cyclones.

Strength

A storm gets a name and is considered a tropical storm at 39 mph (63 kph). It becomes a hurricane, typhoon, tropical cyclone, or cyclone at 74 mph (119 kph). There are five strength categories, depending on wind speed. The highest category is 5 and that’s above 155 mph (249 kph). Australia has a different system for categorizing storm strength.

Kalmaegi is on the stronger side of typhoons, experts said.

The highest tropical cyclone winds recorded were in 2015's Hurricane Patricia in the eastern Pacific, while Typhoon Tip in 1979 had the lowest barometric pressure, which is a key measurement that meteorologists use.

RotationIf they are north of the equator they rotate counterclockwise. If they are south, they rotate clockwise.

Season

The Atlantic and central Pacific hurricane seasons are June 1 through Nov. 30. Eastern Pacific: May 15 to Nov. 30; northwestern Pacific season is close to all year, with the most from May to November. The cyclone season in the south Pacific and Australia runs from November to April. The Bay of Bengal has two seasons April to June and September to November.

Vietnam tends to get landfalling typhoons around this time of year.

The busiest place

The northwestern Pacific where Typhoon Kalmaegi has just hit is the busiest place on Earth because of the year-round warm water, weak upper-level crosswinds and frequent thunderstorm activity that can provide the seeds for storms to form, said Kristen Corbosiero, a professor of atmospheric and environmental sciences at the University at Albany.

By this of year, the Northwest Pacific averages 23 named storms, 14 of which become typhoons, according to Colorado State University's storm database. A normal year there involves 27 named storms. Kalmaegi and Fung-Wong are the 26th and 27th named storms, with Kalmaegi the 15th typhoon. While there slightly more storms than normal, Corbosiero this has been generally a weaker season. The measurement that meteorologists use, which combines storm strength, frequency and duration shows this season is only 62% of average, so far. Kalmaegi is the fourth strongest typhoon this season.

By comparison the Atlantic averages 14 named storms a year and this year there have been 13, with the last one, Hurricane Melissa, causing major destruction in Jamaica and Cuba.

Goosed by a globetrotting weather system

Because the Northwest Pacific has warm enough water to fuel storms practically year-round, the key often is storminess in the atmosphere to be the seed to start something going, Corbosiero said. In this case — and many others — it's an atmospheric disturbance called the Madden-Julian Oscillation, often called the MJO. This is a natural system in the tropics that stars around the Indian Ocean and moves eastward, increasing rainfall and storminess ahead of it and surpressing thunderstorm activity behind it. It can go around the globe in 30 to 60 days.

A strong MJO can trigger tropical cyclone activity and this early summer it did that in the Northwest Pacific but then sort of shut down as the oscillation moved east, Corbosiero said. But a strong one just moved through, helping with these storms formation, she said.

That MJO is now around the international dateline about a week-and-a-half to two weeks away from the Atlantic where it could help spawn late season tropical storms, she said.

How the names are decided

The lists are maintained by the World Meteorological Organization; the names are ones that are familiar in each region. Names are taken off the list and replaced to avoid confusion if a hurricane causes a lot of damage or deaths. For example, Katrina was retired after it devastated New Orleans in 2005. The Philippines has its own naming system, so Typhoon Kalmaegi is also being called Tino.

SOURCES: Colorado State University, University at Albany, Joint Typhoon Warning Center, World Meteorological Organization, National Oceanic and Atmospheric Administration, Weather Underground.

AP video by Jacqueline Hernandez

Produced by Aya Diab

The Associated Press’ climate and environmental coverage receives financial support from multiple private foundations. AP is solely responsible for all content. Find AP’s standards for working with philanthropies, a list of supporters and funded coverage areas at AP.org.