Wind and sea state

When choosing a dive site, wind and sea state plays an important role. In Phuket we have 2 main seasons with different wind directions:

Dry Season
The dry season begins in December and usually lasts until March. The northeast monsoon draws cool, dry air from the Asian continent resulting in a slight drop in temperature. This is the high season for tourism in Phuket, when the climate is at its best, characterized by gentle breezes, calm seas and clear blue skies. It is also the coolest time of year.
Transitional Periods
The transitional periods last a month or so. During these periods the weather is often hard to predict. The period before the rainy season, around April – May, is the hottest time of year. There may be a lot of rain or none at all. The October – November transition is cooler and usually quite wet.
Rainy Season
The rainy season begins in June and lasts until October. When people talk about the monsoon season, they are referring to the southwest monsoon period, which is the rainy season. The strong winds bring warm moist air from the Indian Ocean and plenty of rain. This is Phuket’s low season.

How is the wind affecting scuba diving?

With west or east wind the boat is rolling when traveling to Racha Islands and pitching when travelling to all other dive sites. When the boat pitch passengers will feel more comfortable during the ride.

In dry season with wind from east, waves can’t build up that high as main land is not that far away. Sea state is mostly between calm and slight, rarely moderate and more. In rainy season when wind is blowing from west and south west waves can build up quite high as African continent is far. Therefore wind has time to build waves. What makes Surfers happy at the west coast beaches (Karon, Kata, Patong) is for scuba diving in Phuket a limiting factor. Unpredictable thundershowers in rainy season are the biggest thread for boats. Sea state there can be rough. We operate up to moderate sea state. Forecasts are not that accurate in the tropics. Therefore the final decision which dive site will be dived can only be taken on short notice, sometimes in the morning of the trip. But when we are in doubt we cancel a dive trip free of charge for your comfort and safety.

Wind with tide – smoother water

Wind against the tide rougher water

WMO Sea State CodeWave hightCharacteristics
00 metres (0 ft)Calm (glassy)
10 to 0.1 metres (0.00 to 0.33 ft)Calm (rippled)
20.1 to 0.5 metres (3.9 in to 1 ft 7.7 in)Smooth (wavelets)
30.5 to 1.25 metres (1 ft 8 in to 4 ft 1 in)Slight
41.25 to 2.5 metres (4 ft 1 in to 8 ft 2 in)Moderate
52.5 to 4 metres (8 ft 2 in to 13 ft 1 in)Rough
64 to 6 metres (13 to 20 ft)Very rough
76 to 9 metres (20 to 30 ft)High
89 to 14 metres (30 to 46 ft)Very high
9Over 14 metres (46 ft)Phenomenal
Beaufort numberDescriptionWind speedWave hightSea conditions
0Calm< 1 knot < 2 km/h < 0.5 m/s0 ft (0 m)Sea like a mirror
1Light air1–3 knots, 2–5 km/h0–1 ft (0–0.3 m)Ripples with appearance of scales are formed, without foam crests
2Light breeze4–6 knots, 6–11 km/h1–2 ft (0.3–0.6 m)Small wavelets still short but more pronounced; crests have a glassy appearance but do not break
3Gentle breeze7–10 knots, 12–19 km/h2–4 ft (0.6–1.2 m)Large wavelets; crests begin to break; foam of glassy appearance; perhaps scattered white horses
4Moderate breeze11–16 knots, 20–28 km/h3.5–6 ft (1-2m)Small waves becoming longer; fairly frequent white horses
5Fresh breeze17–21 knots, 29–38 km/h6–10 ft (2-3m)Moderate waves taking a more pronounced long form; many white horses are formed; chance of some spray
6Strong breeze22–27 knots, 39–49 km/h9–13 ft (3-4m)Large waves begin to form; the white foam crests are more extensive everywhere; probably some spray
7High wind, moderate gale, near gale28–33 knots, 50–61 km/h13–19 ft (4-5.5m)Sea heaps up and white foam from breaking waves begins to be blown in streaks along the direction of the wind; spindrift begins to be seen
8Gale, fresh gale34–40 knots, 62–74 km/h18–25 ft (5.5-7.5m)Moderately high waves of greater length; edges of crests break into spindrift; foam is blown in well-marked streaks along the direction of the wind
9Strong/severe gale41–47 knots, 75–88 km/h23–32 ft (7-10m)High waves; dense streaks of foam along the direction of the wind; sea begins to roll; spray affects visibility
10Storm whole gale48–55 knots, 89–102 km/h29–41 ft (9-12.5m)Very high waves with long overhanging crests; resulting foam in great patches is blown in dense white streaks along the direction of the wind; on the whole the surface of the sea takes on a white appearance; rolling of the sea becomes heavy; visibility affected
11Violent storm56–63 knots, 103–117 km/h37–52 ft (11.5-16m)Exceptionally high waves; small- and medium-sized ships might be for a long time lost to view behind the waves; sea is covered with long white patches of foam; everywhere the edges of the wave crests are blown into foam; visibility affected
12Hurricane force≥ 64 knots≥ 46 ftThe air is filled with foam and spray; sea is completely white with driving spray; visibility very seriously affected