Golden Week & Summer Water Temps at Popular Dive Sites

Golden Week in Izu: 17°C and freezing in a wetsuit. Same week in Ishigaki: 26°C in a rashguard. Same country, different planet. Water temps by spot for GW and summer holidays.

Annual Water Temperature Patterns

Let's start with a heatmap view of all seven sites' annual temperature patterns. The contrast between Golden Week (May) and summer (August) is immediately apparent.

Golden Week (Early May) Water Temperatures

During Golden Week, regional temperature differences are dramatic — choosing the wrong suit can make or break your comfort.

Best Golden Week Options

The Kerama Islands are the undisputed winner for Golden Week comfort. A 5mm wetsuit is all you need, visibility consistently reaches 20m, and you may still catch humpback whales at the end of their season.

Kushimoto benefits from the Kuroshio Current, staying 2-3°C warmer than Izu. Still below 20°C most years, so a thick 6.5mm wetsuit with hooded vest can work. Table coral formations are spectacular.

Golden Week on the Izu Peninsula is colder than most people expect. A drysuit is the standard choice. The silver lining: spring turbidity is fading and visibility is improving.

Echizen during Golden Week is still very cold, with visibility near its annual low. The Sea of Japan peaks in summer (July-September), so Golden Week is not ideal.

Summer Vacation (July-August) Water Temperatures

Summer brings peak water temperatures nationwide, making wetsuit diving possible at virtually every site. However, temperatures vary by more than 5°C between regions.

Izu in summer sits at 23°C — surprisingly 4-5°C cooler than Okinawa or Echizen. A 5mm wetsuit is recommended. Watch for thermoclines — water below 10m can drop sharply.

Echizen transforms in summer, reaching around 25°C. The Tsushima Current brings warmth and peak annual visibility.

Ishigaki is among Japan's warmest, approaching 29°C. Sun protection is more important than thermal protection. Summer is prime manta ray season.

Monthly Temperature Trends

The chart below shows how water temperature evolves at each site. Note the steep rise from Golden Week (May) to summer vacation (August).

Recommendations by Category

Budget Pick: IOP (Izu Oceanic Park)

Accessible as a day trip from Tokyo by train or bus. GW requires a drysuit, but summer is comfortable in a 5mm wetsuit. Low cost with diverse marine life.

Luxury Choice: Ishigaki & Kerama

Flight and accommodation costs are significant, but 28°C+ water and 20m+ visibility is unmatched. Even during Golden Week, Kerama is comfortable in just a 5mm wetsuit.

Hidden Gem / Best Value: Echizen

Easily accessible from Nagoya and Osaka. Summer brings warm water and peak visibility without the Okinawa price tag (note: GW is too cold here — summer only).

Suit Selection Guidelines

• 28°C+: 3mm wetsuit or rashguard
• 24-28°C: 3-5mm wetsuit
• 20-24°C: 5mm wetsuit + hood vest
• 16-20°C: 6.5mm wetsuit or drysuit
• Below 16°C: Drysuit recommended

PADI recommends proper exposure suit selection as fundamental to diving safety and comfort.

Use Our AI Forecast

The temperatures above are historical averages. Some years, Izu drops to 14°C during Golden Week; other years it reaches nearly 19°C. Our AI water temperature forecast predicts site-specific temperatures up to 7 days ahead with 92% accuracy and ±0.67°C error. Check the forecast before packing your gear.

Summary

Water temperature differences between sites are dramatic during Golden Week and summer. For Golden Week wetsuit diving, Okinawa is the clear choice. In summer, wetsuit diving is comfortable nationwide. Check the forecast, choose the right suit, and enjoy safe, comfortable diving.