Thunders seasonal overview
Best Surf Season (May - September)
Thunders is a classic Indonesian west-southwest-facing reef setup, exposed to the full force of the Southern Ocean and Indian Ocean swell machine. The months from May through September deliver the most consistent combination of groundswell and clean wind. During this window, the average swell height climbs from 1.5m (4.9ft) to 1.7m (5.6ft) while the average period sits at a powerful 13.9-14.3s. The seasonal shift to the southeast trades dries out the atmosphere and, more importantly, keeps the northwest monsoon winds at bay. This allows the SSW and S swells, which are dead on the exposure, to break with real shape on Thunders' west-facing reefs.
July and August are the standout months: long-period S/SSW pulses hit at 1.5-2m (5-6.5ft) as standard, and a meaningful share of days push into the overhead 6-8ft (1.8-2.4m) range. With water temperatures around 29-30°C and air temps near 28°C, it is tropical perfection. Expect offshore/cross-offshore morning winds, glassy surface, and pumping, reeling lines.
Fair Surf Season (March - April & October - November)
The transition months around the heart of the surf season provide a mix of good and forgettable. Swell size sits at a solid 1.3-1.5m (4-5ft) with long-period 12.8-13.5s energy arriving from the SW-SSW, but the wind patterns are caught between monsoons. The percentage of ideal winds runs between 39 and 46 percent, meaning a decent number of mornings are clean and offshore before sea breezes or crosswinds mess with things. When the trade winds return or the rain squalls clear out, Thunders can still showcase excellent, rippable waves.
These months are worth chasing for the sneaker days: a strong Southern Ocean low will spin up late-period SSW swell while the local winds align from the east/northeast, producing glassy, grinding conditions.
Low Surf Season (December - February)
December through February is the least consistent stretch for quality at Thunders. The northwest monsoon is in full swing, bringing humid, showery conditions and frequent W to NW winds. While the swell window remains active - average heights still hover around 1.3m (4.3ft) and periods stay in the 12.2-12.5s range - those onshore/cross-onshore winds chop up the surface and turn otherwise good waves into a battle. Only 26-27 percent of the time are the winds ideal for surfing.
That said, this is Indonesia, not a flat spell. Periods between monsoon squalls often deliver clean, powerful SSW/SW groundswell under light east/northeast winds. If you are flexible and willing to wait for a window, you can still find fun, hollow waves. It is simply not the reliable, world-class consistency of the dry season.