Porto
9.1normal hot days across June–August*
Porto / Pedras Rubras
XPATUS study · 2 stations
Lisbon and Porto: how monthly averages can hide hot days
Neither station has a monthly mean above 30°C. Yet the sum of normal hot-day counts for June–August is 9.1 in Porto and 24.4 in Lisbon: days with a daily maximum of at least 30°C. The difference is 15.3 days. A monthly mean does not tell you how many hot days that month contains.
These are 1991–2020 normals for two specific stations, not a forecast or a description of every neighborhood. IPMA series combine observations and locally modeled WRF data. This comparison does not assess humidity, heatwaves, indoor comfort or relocation suitability.
Published and sources verified: · Climate period: 1991–2020
Days reaching 30°C: June–August
Numbers sum the long-term monthly averages, not the number of days promised for your next trip. Both bars use a 0–30 day scale.
Lisbon
24.4normal hot days across June–August*
Lisboa / Instituto Geofísico
*The threshold applies to the maximum on an individual day (≥30°C); the average applies to the count of these days over the normal period. This is not the average summer daily maximum.
What monthly means tell us
Porto
Coolest month, January: 10.2°C
Warmest month, August: 20.2°C
Span of monthly means: 10.0°C
Months with a mean above 20°C: 1
Months with a mean above 30°C: 0
Lisbon
Coolest month, January: 11.8°C
Warmest month, August: 23.8°C
Span of monthly means: 12.0°C
Months with a mean above 20°C: 4
Months with a mean above 30°C: 0
Means above 20°C: only August in Porto; June–September in Lisbon. A monthly mean includes cooler nights: hot-day counts cannot be inferred from it.
All 12 months, with the input data
Mean is the monthly average of daily mean temperature; hot days are the average count with a daily maximum ≥30°C. The table scrolls horizontally on narrow screens.
| Month | Porto | Lisbon | ||
|---|---|---|---|---|
| January–December | Mean, °C | Hot days | Mean, °C | Hot days |
| January | 10.2 | 0.0 | 11.8 | 0.0 |
| February | 10.9 | 0.0 | 12.8 | 0.0 |
| March | 12.9 | 0.0 | 14.9 | 0.0 |
| April | 14.1 | 0.1 | 16.3 | 0.1 |
| May | 16.3 | 1.1 | 18.8 | 2.1 |
| June | 18.6 | 2.5 | 21.5 | 5.7 |
| July | 19.9 | 3.1 | 23.2 | 8.5 |
| August | 20.2 | 3.5 | 23.8 | 10.2 |
| September | 19.2 | 2.2 | 22.1 | 5.7 |
| October | 16.8 | 0.4 | 19.1 | 0.9 |
| November | 13.1 | 0.0 | 15.0 | 0.0 |
| December | 11.1 | 0.0 | 12.4 | 0.0 |
Rounding matters: Porto’s 12 monthly hot-day values sum to 12.9, while IPMA’s annual column is 13.0. A sum of rounded months must not be presented as the source’s exact annual normal.
Sources, calculations and inclusion rules
Of three Portugal locations in our planning cohort, two complete IPMA records share a period and version. Faro is excluded: its NASA POWER record uses a regional grid and the 2001–2020 period. This is not a Portugal or worldwide ranking.
- IPMA · Porto / Pedras Rubras · 1991–2020 · 1.0/2024
- IPMA · Lisboa / Instituto Geofísico · 1991–2020 · 1.0/2024
- IPMA: normals and indicator definitions
XPATUS calculation: span = maximum minus minimum of the 12 monthly means; month counts use a strictly-greater-than threshold; summer hot days sum June, July and August. Temperature spans and sums are shown to one decimal place.
This is an original calculation and presentation of IPMA data, not new measurements. The series are hybrid and homogenized; IPMA may revise them after quality control. We assign no new license to the underlying data: attribute IPMA and consult the provider’s reuse terms.