(I'm mostly replying to this entire thread rather than Owain's comment.)

I'm failry confident in the following two claims:

Warm climate slows down transmissions substantially.
But not enough to prevent large outbreaks.

My reasoning being:

As commenters have pointed out, we see striking correlations between countries that report large numbers of cases and cold-ish temperatures.
The alternative hypothesis (poorer testing and detection) seems likely true to me, but not strong enough to overcome this point:

Now granted there could be a higher spread in these countries that is underreported, but if they had it bad as in Italy or Iran it wouldn't go unnoticed.

That said, I think there is circumstantial evidence for a somewhat large underreported outbreak in Indonesia (avg temperature of 31+ Celsius for the last two months), and maybe also the Philippines (but I haven't been following the latter at all). For Indonesia I think it's likely they have upward of 2,500 infections. It seems implausible to me that they'd already be anywhere near Italy or Iran's level of infections, but if one is really cynical, I admit that it can't be ruled out completely.

Some relevant data points:

When Indonesia had <20 confirmed diagnoses, 3 Indonesians were tested positive abroad: a married couple in Singapore and an Indonesian woman who travelled to Australia. The Singapore case seems to have been motivated by seeking quality hospital care, which admittedly makes this evidence consistent with a smaller outbreak than if Indonesians who travelled to Singapore for non-health-related reasons had tested positively. Still, I think 2 instances of testing positive abroad at a time when the official count is <20 is quite telling.
Indonesia also reported 4 deaths by now. For the first death, a British woman age 53 with several serious previous health conditions, Indonesian authorities labelled the case "imported" because the woman had only been to Indonesia for a couple of days by the point she died. However, I'm not sure whether I should believe the conclusion because there were reports (US nursing home and one from Italy) of people going from symptomatic to dead in <30h. In any case, 3 further deaths were announced yesterday, and no indication was given that they might be imported cases. Even just 3 deaths usually correspond to true rates of infection well above 1,000. The ratio of confirmed diagnoses to deaths is now exceptionally high in Indonesia. (The same applies even more strongly to the Philippines, but I could imagine that some deaths there were definitely imported.)
There was this entire discussion about expert modelling suggesting that indonesia's long count of zero diagnoses is evidence for them missing cases throughout February.
(Indonesia was one of the last countries to ban incoming travel from Italy or Iran, I believe.)
According to this tweet, testing in Indonesia was 970 people. Indonesia's population is >>200 million.

In addition, the incentives for reporting cases diligently seem to be suboptimal, as evidenced by some data points:

Indonesian ministers install even less confidence than Trump. Just one example of communication: About the Australia exported case, the Indonesian health official claimed that the woman most likely got infected in Australia because she had travelled for quite a while and because she also visited a Vietnamese restaurant there (implication: Vietnamese restaurants in Australia are risky). However, the Australian source (link above) says clearly that the woman in question started showing symptoms 2 days after leaving Jakarta (so much for "she travelled for quite a while"), and the only reason a Vietnamese restaurant was mentioned anywhere is because the Australian authorities obviously traced the Indonesian woman's contacts in order to interrupt a potentially newly started chain.
Maybe the time lag confuses me, but I'm pretty sure there was one time when Indonesia skipped a day of reporting case numbers, and then numbers double and deaths went from 1 to 4. (Could be totally benign if there's some disorganization during a time of crisis, of course.)
Indonesian officials seem to be under enormous pressure because the economy is doing very poorly already. Some unusual measures have already been taken a while back, such as disallowing shorting and pledges for government-owned companies to buy back shares.

And here's a concerning but speculative hypothesis:

Singapore doctors gave out a warning that patients who tested positive for Dengue fever with a quick-testing kit actually turned out to have Covid-19. They say the diseases are clinically similar and that the widely used quick-test kits may not have failed isolatedly due to extraordinary circumstances. Indonesia currently has a somewhat large Dengue outbreak (and the same goes for the Philippines).

UPDATE: 18 days after I made this comment, Reuters reports that Jakarta's funeral count for March was 1,300 funerals higher than any preceding month since 2018. This looks highly statistically significant because the previous record was only 3,100 (compared to 4,400). (And there was no natural disaster or other unusual disease outbreak.)