BMKG Classifies 2.5-Metre Waves as High, Not Extreme

Labuan Bajo — The Meteorology, Climatology and Geophysics Agency (BMKG) classifies significant wave heights of 2.5 to 4 metres as high, 4 to 6 metres as very high and above 6 metres as extreme, according to its maritime warning pages.

BMKG’s national warning page showed 44 maritime areas in the high category and 162 in the moderate category for a warning valid from 16 September 2026 at 07.00 WIB to 19 September 2026 at 07.00 WIB. The same page showed no areas in the very high or extreme bands.

For travellers and boat operators around eastern Indonesia, the important point is that BMKG’s warning system is area-specific, not a blanket label for an entire province or island group. Conditions can differ between nearby waters, so a route should be checked against the named sea area and the warning’s validity period.

What the categories mean

BMKG’s published wave-height bands are:

• Moderate: 1.25 to 2.5 metres
• High: 2.5 to 4 metres
• Very high: 4 to 6 metres
• Extreme: above 6 metres

That means the boundary between moderate and high is 2.5 metres, while 4 metres marks the start of the very high category. BMKG presents these categories in its maritime warning display for forecast significant wave height.

An independent report from RRI on 15 September 2026 said BMKG was warning of waves of 2.5 to 3.5 metres in the southern waters of Sumba, with 1.25 to 2.5 metres also possible in several other NTT waters, including Selat Ombai, northern Timor, northern Kupang and Rote, and southern Rote. That report supports the broader point that BMKG warnings for NTT can vary by named waterway.

Why the named waters matter

The BMKG extract available for 16 to 19 September did not identify NTT waters in the summary text shown in the warning page snippet, and the separate maritime page only shows the national category totals. For that reason, the confirmed fact is BMKG’s classification of wave-height bands, not a province-wide rule for all of NTT.

In practical terms, passengers should ask which BMKG maritime zone covers the crossing, and whether the warning applies to the scheduled departure and return windows. That matters for routes serving Labuan Bajo, Komodo and other parts of Flores and the wider NTT chain, where conditions may differ from one sea area to another.

BMKG says its maritime warning information is intended to help users assess expected wave height during the validity period. The agency’s categories are based on forecast significant wave height, so the number shown is the key figure for deciding whether a route is in the moderate, high, very high or extreme band.

For now, the verified takeaway is simple: 2.5 metres is the threshold BMKG uses to define high waves, while anything above that moves into more dangerous categories. Separate BMKG messaging for NTT waters shows why route-by-route checking is essential before sailing.

Sources

• BMKG - Peringatan Gelombang Tinggi - Cuaca
• RRI Ende - BMKG Waspadai Gelombang Tinggi hingga 3,5 Meter