In Sumba, an Indonesian island belonging to the group of the Lesser Sunda Islands, the climate is tropical, hot all year round, with a rainy season from December to March, and a dry season from June to October. In the rainy season the sun shines for a few hours a day, in fact it usually rains a couple of hours in the morning and a couple of hours in the afternoon.
Temperatures are high and uniform throughout the year. They are slightly higher from October to May, and a bit lower from June to August. The hottest days of the year, with highs about 35/36 °C (95/97 °F), are often recorded in October and November, before the rainy season. In the latter, high relative humidity makes the heat muggy.
Here are the average temperatures of the airport, located near Waingapu.
Waingapu - Average temperatures
MonthJanFebMarAprMayJunJulAugSepOctNovDec
Min (°C)242424232321202021232424
Max (°C)323232323131313132333333
Min (°F)757575737370686870737575
Max (°F)909090908888888890919191

The rains are not very abundant, and generally amount to 1,200/1,400 millimeters (47/55 inches) per year, but there are also some areas where rainfall drops below 1,000 mm (40 in), such as that of Waingapu, located on the north coast. Given that the rains are abundant only from December to March, and that the dry season is quite long, the landscape is not particularly verdant, in fact in some areas it is almost arid. Here is the average rainfall in Waingapu.
Waingapu - Average precipitation
MonthJanFebMarAprMayJunJulAugSepOctNovDecYear
Prec.(mm)17016014570352510551040135810
Prec.(in)6.76.35.72.81.410.40.20.20.41.65.331.9
Days131311964311261180

In Sumba there's plenty of sunshine in the dry season, while in the rainy season the sun shines for a few hours a day, between a rainshower and the other.
Waingapu - Sunshine
MonthJanFebMarAprMayJunJulAugSepOctNovDec
Hours667999910101087

From November to mid-May, but more often from January to mid-April, Sumba can be affected by tropical cyclones, which are formed on the sea of Timor, and then move south-westard, between the Sunda Islands and Australia.
In the interior of Sumba there are hills that reach about 1,000 metres (3,300 feet). In some areas there are tropical forests and waterfalls.

Ratenggaro

The sea in Sumba is warm enough to swim in throughout the year: the water temperature goes from 29 °C (84 °F) from November to April, to 26/27 °C (79/81 °F) from July to September.
Sumba - Sea temperature
MonthJanFebMarAprMayJunJulAugSepOctNovDec
Temp (°C)292929292828272627282930
Temp (°F)848484848282817981828486

When to go


The best time to travel to Sumba and enjoy its beaches, goes from June to August: the sun shines, the heat is not too intense, and in any case it's tempered by the breeze; there are just some short downpours or thunderstorms every now and then. In September it is often very hot. At the end of September or in October the rains begin to increase in inland and hilly areas.

What to pack


All year round, light clothes, of natural fibres, a sun hat, a scarf for the breeze, a light sweatshirt for the evening (especially from June to September). From December to March, a light raincoat or umbrella.