Alor’s surface water sits at a comfortable 26–29°C for most of the year, but the region’s defining feature is its thermoclines: at southern and deeper Pantar Strait sites, upwellings can drop the water to 20–22°C in a few metres of descent, with occasional plunges toward 16°C. The practical answer for most divers is a 3 mm suit for the northern reefs and a 5 mm — or 3 mm plus hooded vest — for the pelagic walls in the September–November season.
Why Alor runs hot and cold at once
Alor sits between two seas with different personalities. The northern sites around Pura and the upper Pantar Strait hold tropical-standard 27–29°C. But the straits are deep channels connecting the Banda Sea to the Savu Sea, and during the east monsoon they pump cold, nutrient-rich water up from depth. That upwelling is the engine of everything Alor is famous for — the fish density, the hammerheads, the visibility — and the thermocline is simply the engine room’s temperature.
Month by month
| Months | Typical water | Thermocline behaviour |
|---|---|---|
| December–March | 28–30°C | Warm and uniform; rainy season, fewer boats |
| April–July | 26–29°C | Occasional mild thermoclines; calmest, most comfortable diving |
| August–November | 22–28°C | Pronounced cold layers at 15–35 m on southern/deep sites; peak pelagic season |
The pattern to internalise: the coldest water and the best big-animal diving are the same thing. Divers who want warmth pick April–June; divers who want hammerheads accept the chill. The best-time guide works through that trade-off month by month.
What crossing a thermocline is actually like
It is abrupt. The water shimmers like heat-haze over a road, and one fin-kick later the temperature has dropped six degrees. On a hammerhead wall in October you might descend through 28°C surface water and settle into 21°C at 25 m for half the dive. Cold is a safety variable, not just comfort: chilled divers burn gas faster, think slower, and abort earlier — which is why exposure protection appears in our safety standards rather than being left to bravado.
The wetsuit decision, settled
- April–July, northern reef itineraries: 3 mm full suit for most divers; warm-blooded divers manage in less.
- September–November, pelagic itineraries: 5 mm full suit, or 3 mm with hooded vest. Add a hood — heat loss at the head is the difference-maker at 21°C.
- Snorkellers: a 2–3 mm shorty covers the surface layer, which stays warm even in upwelling season.
- Cold-prone divers doing 3–4 dives daily: err one thickness up. Repetitive diving compounds chill in a way single dives never show.
Full kit logic — including what the boat carries and what you should not waste luggage weight on — is in the packing guide.
Visibility rides the same system
The upwelling that chills the water also feeds it. Dry-season visibility commonly runs 20–30 m; in the deepest upwelling weeks it can dip where plankton blooms — the price of the food chain that pulls in the animals. December–February drops toward 10–15 m with the rains.
Divers who have worked cold thermoclines at Komodo’s southern sites — home ground of the Pinta Liveaboard crew — will find Alor’s version familiar: same monsoon engine, same rule that the cold edge is where the life is. Pack for the thermocline, and the strait pays it back with interest.
Quick questions about temperature planning
Can I get away with a 3 mm in October?
On the northern reefs and in the bays, yes. On the southern walls and seamounts — the dives October is booked for — you will be counting minutes once the thermocline finds you. The upgrade that changes everything is cheap and small: a hooded vest under the 3 mm turns a shivering dive into a comfortable one, and it packs flat.
Do thermoclines affect safety stops?
Usually the opposite — the cold water sits deep, and your 5 m stop happens in the warm surface layer. The place cold bites is mid-dive, at the 20–35 m watching depths, which is exactly where you want to be relaxed and slow-breathing. Dress for the coldest ten minutes of the profile, not the average.
Is the water ever too cold to dive?
No — the extremes are brief plunges within otherwise tropical dives, not sustained cold-water diving. The 16°C readings that appear in logbooks are momentary pockets at depth on the strongest upwelling days. Alor never requires drysuit thinking; it requires one honest layer more than the brochure photo suggests.