Two seasons, not four
musim hujan ‘rainy season’, roughly October to April
musim kemarau ‘dry season’, roughly May to September
Musim also covers seasons in the sense of periods: musim durian is durian season, musim liburan is holiday season.
Rain
hujan ‘rain’
hujan deras ‘heavy rain’
gerimis ‘drizzle’
mendung ‘overcast’
badai ‘storm’
Lagi hujan. ‘It’s raining.’
Hujan terus. ‘It keeps raining.’
Note there is no dummy subject. English needs “it”; Indonesian just says rain.
Heat and humidity
panas ‘hot’
gerah ‘muggy, sticky’
lembap ‘humid’
sejuk ‘pleasantly cool’
dingin ‘cold’
Gerah is the one worth learning. It describes still, sweaty heat with no breeze, and it is what people actually complain about rather than panas.
Why this is logistics
In rainy season it rains hard for an hour or two, usually in the afternoon, and then stops. This governs when people travel, whether a motorbike is a good idea, and how long a journey takes.
Banjir ‘flood’ is a normal part of the vocabulary in Jakarta and low-lying areas, not an exceptional event.
Jalannya banjir. ‘The road is flooded.’
Macet karena hujan. ‘Traffic’s bad because of the rain.’
Asking
Cuacanya bagaimana? ‘What’s the weather like?’
Nanti hujan nggak? ‘Is it going to rain later?’
Expect a confident answer that is not necessarily a forecast, in the same spirit as the directions lesson.
What you’ll actually hear
What the book says: Cuaca hari ini sangat panas dan lembap.
What you’ll hear: Gerah banget hari ini.