When people reach for a comparison to the current dry season in South-East Asia, they reach for 2018–19. It is the wrong comfort. By the headline ocean index that cycle was the stronger El Niño — and yet Thailand’s three-month water balance stayed positive through it. In the May 2026 update it does not. The label got weaker; the ground got drier.
The two cycles, side by side
SPEI-3 measures the last three months of water balance against the same season in the historical baseline. Zero is normal for the time of year; negative is drier than that baseline; readings past −0.5 are conventionally treated as drought conditions.
| Indicator | May 2026 | 2018–19 analog |
|---|---|---|
| Thailand — SPEI-3 mean | −0.288 | +0.135 to +0.703 |
| Vietnam — SPEI-3 mean | −0.487 | wetter than 2026 |
| Malaysia — SPEI-3 mean | −0.398 | wetter than 2026 |
| Headline ocean index | RONI +0.47 (Neutral) | ONI ~0.8–0.9 |
Thailand is the row with a number on both sides, and it is the row that matters most. Through the 2018–19 cycle its three-month balance ran between +0.135 and +0.703 — wetter than the historical baseline for the season, across the range. In May 2026 the same measure reads −0.288. That is not a small move along a scale; it is a change of sign.
For Vietnam and Malaysia the 2026 readings are the harder ones — −0.487 and −0.398 — and the analog review that supplies the comparison places both cycles in the same direction: 2018–19 was the wetter of the two. We are publishing that as a direction rather than a number, because a single verified figure for those two countries in the analog period is what we have not got. A direction we can stand behind is worth more than a decimal we cannot.
A stronger headline over wetter ground
By the Oceanic Niño Index, the sea-surface measure that drove most 2018–19 coverage, that cycle ran around +0.8 to +0.9 — unambiguously an El Niño event by the number everyone quoted. The 2026 picture is the reverse. The current official index is the Relative Oceanic Niño Index, and for April–June 2026 it reads +0.47. The threshold is +0.50. By the index of record, this is Neutral — not an El Niño.
So the comparison lands like this. The cycle with the stronger ocean signal left Thai soil wetter than normal. The cycle that does not qualify as an event at all has all three countries below their baseline. Whatever is drying the region in 2026, the headline index is not the thing that would have told you about it.
Why the label is not the risk
An ENSO index is a measurement of the ocean. It is a good measurement, and it carries real forecasting skill at regional scale and seasonal range. What it is not is a measurement of the field, the reservoir, or the loan book. Those live at sub-national scale, and the 2018–19 comparison is the cleanest demonstration we have that the two can move apart: a strong label and a wet ground in one cycle, a neutral label and a dry ground in the next.
The practical failure mode is a planning cycle that waits for the label. If a portfolio review is triggered by the words “El Niño declared”, then in 2026 it has not been triggered — because by the official index there is nothing to declare — while the water balance across three countries has already gone negative. The trigger was attached to the wrong variable.
What a baseline is actually for
The point of holding both cycles side by side is not to argue that 2026 is worse in every respect. It is to fix a reference. Analog reasoning is only as good as the analog: if the last event most people remember left the ground wetter than normal, then “this looks like 2018–19” is a statement that understates the current position rather than describing it.
For anyone carrying exposure across Thailand, Vietnam or Malaysia, the more useful question is not which ENSO phase we are in but what the three-month water balance reads where the exposure actually sits — and how that compares to the same month in the years already survived. That is a question sub-national data answers and a headline index does not.
One caveat we will not paper over: these are May 2026 readings, and the drought pipeline updates monthly. A single month is a position, not a trajectory. The comparison above is about where the two cycles stood, not where this one is going.
The province-level drought picture behind these figures is at globmaps.com.