Iriomotejima

Station

This file uses JMA's special regional weather station on Iriomote (西表島, block 47917). It records wind and every other element on this page. It stands 10.3 m above sea level at Sumiyoshi near Uehara on the north coast. The island's other JMA point is the Ohara AMeDAS station (block 1251) on the south-east coast, and it has no humidity normals. Every figure in this file is JMA's published 1991–2020 normal, and rain days count the days with 1 mm or more.

Winter

North-east is the most frequent wind at the Iriomote station in every month from September to May, averaging 4.6–4.8 m/s from December to February. At Ohara on the south-east coast the winter wind comes most often from the north-north-east, in 26–31% of observations from December to February. December gets only 70.7 hours of sunshine and January 71.8, and rain falls on 12.0 to 14.1 days a month from December to March.

Spring

In early spring a low from the East China Sea sometimes deepens fast as it crosses Okinawa. Once its cold front passes, a southerly wind swings round to a strong north or north-east wind and the temperature drops. Okinawans have long called this *ningwachi kajimaai* (the wind turn of the second lunar month).

Summer

When the rainy season ends in late June the Pacific high pushes west and a strong south to south-west wind called *kaachiibee* blows steadily for several days. The Iriomote station's most frequent wind from June to August comes from due south.

Typhoon

JMA counts a typhoon as approaching the Okinawa region when its centre comes within 300 km of a station there, and the 1991–2020 normal is 7.7 approaches a year. August averages 2.2 approaches and September 1.9. Across those 30 years JMA recorded no approach at all from January to March.

Rainy

JMA's 1991–2020 average puts the start of Okinawa's rainy season around 10 May and its end around 21 June. JMA's preliminary dates for 2026 were around 4 May and around 29 June. Okinawans call the season *suuman boosuu* after two of the old solar terms that fall inside it.

Sea

Sea temperatures are our monthly averages of JMA's daily 1991–2020 sea surface normals at its fixed point north of Ishigaki (石垣島北). The monthly figure runs from 23.2 °C in February up to 29.4 °C in July. We use it because the Iriomote station sits on the north coast, and by our comparison JMA's point south of Ishigaki runs within 0.3 °C of it in every month.

Wind

The windDir field holds JMA's most frequent wind direction (最多風向) for each month as the 16-point compass point the wind blows from.