IPMA Calls a Hot, Showery 1.º de Maio Long Weekend With 28°C in Beja and 31°C in Santarém — Bragança, Castelo Branco and Guarda on Yellow Rain Alert as Above-Normal Temperatures Run Through 17 May

The Instituto Português do Mar e da Atmosfera lifted Portugal's three-day forecast on Thursday afternoon, calling a warm and unstable opening to the 1 May long weekend. With 1.º de Maio falling on a Friday and producing the country's first proper bridge-weekend of the season, the forecast is the most useful piece of practical reading mainland residents will pick up before Saturday morning.

The Weekend Numbers

Maximum temperatures on Saturday, 2 May, peak in the southern interior: 28°C in Beja and Santarém, with the rest of the Alentejo basin tracking close behind. Sunday, 3 May, lifts further on the western flank: Santarém is forecast at 31°C, Beja holds at 28°C, and the Tagus valley between Santarém and Lisbon sees the first sustained early-summer-style heat of the year. The Atlantic coast remains cooler — Lisbon in the low-to-mid 20s, Cascais and Estoril a degree or two below — and the northern coastal strip runs cooler still.

Showers and Thunderstorms in the Interior

IPMA's forecaster on the case, Ângela Lourenço, called Saturday with showers and thunderstorm activity in the interior and stronger winds in the higher terrain. Sunday afternoon picks up similar activity, with thunderstorms most likely in the mountain ranges — Estrela, Marão, Larouco — and the Beira interior. The interior-coastal split is the textbook April-May pattern in Iberia: a warm-air-mass advection from the south-west builds afternoon convection over the Meseta and the eastern mountains while the Atlantic stays stable.

Three districts open the weekend on a yellow rain advisory: Bragança, Castelo Branco and Guarda. Yellow is the lowest of the three IPMA advisory tiers (yellow, orange, red) and signals expected weather conditions that may produce localised impacts — wet roads, brief flash flooding in low points, and reduced visibility on the IP2 and IP4 corridors.

The Bigger Picture: a Warm Spell Through 17 May

The seasonal-bulletin overlay from IPMA's medium-range modelling has temperatures running above the 1991–2020 climate normal through 17 May, with a particularly warm anomaly along the Spain-Portugal interior border. The agency has flagged the run as the kind of pattern that begins the fire-prevention season early; the Interior Ministry's Civil Protection update earlier this week included its first situational read for what officials have privately described as a "terrible summer" of fire risk, and the May warm spell is the first observational evidence in that direction.

What This Means for the Long Weekend

• Bridge-weekend trips into the Alentejo and Algarve get sun and pool weather — but if you are on the Évora-Beja-Mértola axis, plan around afternoon thunderstorms on both Saturday and Sunday.
• Trail running, mountain biking and the Estrela ski-pista's transition season: avoid exposed ridgelines on Saturday afternoon. Lightning strikes in the Serra da Estrela above 1,500m are the regular cause of mid-spring outdoor accidents in the country.
• Beach trips on the Costa Vicentina and Algarve see warm but breezy conditions; sea-water temperatures are still in the 16–17°C range, ahead of the formal Blue Flag opening of the bathing season on 3 June at Santa Cruz da Graciosa.
• Allergy sufferers: the warm-and-windy combination is the worst-case profile for grass-pollen exposure. SPAIC's national pollen alert runs in parallel through 7 May.
• Driving on the IP2 and IP4 corridors through Bragança, Castelo Branco and Guarda: yellow advisory means slow-down conditions on Saturday afternoon. The IPMA app and IP-Estradas variable-message-sign network will publish real-time updates.