El Nino Watch
A natural see-saw of ocean temperature and winds in the tropical Pacific. It has three phases: El Nino (warm), La Nina (cool) and neutral.
El Nino basics
ENSO is the name scientists use for one big climate pattern with two halves:
The two halves push on each other. Warmer water weakens the winds; weaker winds let even more warm water spread east. That feedback is why an El Nino can grow for months and then last most of a year.
ENSO is natural. It existed long before modern climate change. Episodes typically come back every 3 to 5 years, but the gap has varied from 2 to 7 years in the record.
The phase is read from the sea surface temperature in the Nino 3.4 region: +0.5 °C or more above normal for several months = El Nino, -0.5 °C or less = La Nina, in between = neutral. The atmosphere must also respond (winds, pressure, rain) for an official declaration.
ENSO is the single biggest reason why one year in Thailand is drier or wetter than the next. It does not decide tomorrow's weather on Koh Samui, but it tilts the odds for whole seasons.