hot sia

Singapore · every HDB block

Will tonight be too hot to sleep?

hot sia! tells you by 5 pm, block by block. And what to do about it.

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In testing on Android and iOS · sample data for now

hot sia!5:05 pm

Tonight at Blk 1 Bedok Sth Ave 1

Hot spell

A hot night tonight

80% chance of 2 or more hot nights in the next 3

Stay in a cool room. Turn on the air-con or a fan.

The Tonight screen. Sample data, not a forecast.

Heat warnings sleep at night.

Of 405,439 NEA heat-stress readings taken after 8 pm, not one rose above Low.1

The advisory is built for daytime outdoor exercise. A hot bedroom at 3 am is outside its job.

More than 1 in 3 nights stayed hot in 2024.

Twice the share of 2022. Each stripe is a year; darker means more hot nights.1

Share of station-nights that stayed at or above 27 °C, by year
YearShare of hot nights
26.1%2016
23.1%2017
21.5%2018
29.8%2019
20.0%2020
19.1%2021
17.9%2022
31.1%2023
35.7%2024

Night minimum from 8 pm to 8 am at 10 NEA stations at or above 27 °C, our alert setting (not a health limit). 2016 has fewer recorded nights.

69,650

seniors live in HDB 1–2 room flats.3

2 in 3 homes in 1–2 room flats have no air-con (67.4%).4
An older adult and a caregiver walk through an HDB void deck at dusk.
An illustrative evening scene in an HDB estate.

From 5 pm to 8 am, someone is watching the night.

  1. 5:05 pm

    Every block gets a level

    A forecast for all 10,796 HDB blocks.2 Families who follow a block get an alert.

  2. 8 pm – 8 am

    Act on one clear step

    Stay in a cool room. Turn on the air-con or a fan. Call your parents.

  3. 8:00 am

    Care staff go knocking

    Active Ageing Centres get a ranked list of blocks to check on.

  • Low A normal night
  • Warm night Stay cool
  • Hot spell 2+ hot nights ahead

Catches 7 in 10 hot nights.

NEA's forecast low catches 6. Same number of alerts, 7 years it had never seen.5

Share of hot nights caught at equal alerts, 2018–2024
MethodHot nights caught
hot sia!70.2%
"Last night was hot"61.8%
NEA forecast low60.4%

Won every test year

  • 2018
  • 2019
  • 2020
  • 2021
  • 2022
  • 2023
  • 2024

Each year forecast by a model trained only on earlier years. Beat both NEA's forecast and "last night was hot" in all 7. +8.5 points over "last night was hot" (95% CI +6.2 to +10.6).5

Know which doors to knock on.

  • A morning check-in list, with the reason for each block
  • A map of every block and area
  • An Advisory Designer to set how often alerts go out

Check-in listReplay: 26 Aug 2024

BlockRental flatsHot spell
Blk 37 Circuit RdGeylang45286%
Blk 52 Cassia CresGeylang49375%
Blk 603A Tampines Av 9Tampines44773%

76 blocks · 12,832 rental flats to check that morning6

The staff dashboard, replaying a real night from our backtest.

Tonight, check on the people who matter.

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Sources and methods

6 notes
  1. NEA air temperature and WBGT via data.gov.sg; our analysis (docs/plan/facts.md, ml/work/log_26.txt, log_28.txt).
  2. HDB Property Information via data.gov.sg.
  3. SingStat, residents by planning area, age and dwelling type, June 2026; summed by us.
  4. SingStat Household Expenditure Survey 2023, p. 67: 32.6% of 1–2 room households own air-con.
  5. Our out-of-time backtest, 2018–2024, 22,274 station-nights, against the NEA 24-hour forecast (bias-corrected by us) and a persistence rule (ml/work/log_32.txt).
  6. Out-of-time forecast replayed for 26 Aug 2024 (docs/plan/facts.md, slide 3).