Effects of Storm Ana in Portugal
2017-12-12 (IPMA)
On December 10th, 2017, a depression, which was designated storm Ana, moving eastward in the North Atlantic, deepening rapidly, with a maximum pressure drop of 24 hPa in its center in 12 hours, between 12UTC on 10th and 00UTC on 11th December (Figure 1).
At 12UTC on 10th December, Storm Ana was slightly northeast of the island of S. Miguel, in the Azores, at a distance of 870 km approximately from Viana do Castelo, with about 988 hPa of minimum pressure in its center. This depression moving quickly to the east, deepening, located to the northwest of the Iberian Peninsula, at 18 UTC, and in the Bay of Biscay, at 00UTC on 11th December, both positions about 500 km from Viana do Castelo. In this path the pressure in the center of the depression drops to 964 hPa at 00UTC (Figure 1c, d).
The cold front associated to storm Ana, approaches mainland Portugal in the late afternoon of the 10th, reaching the north of the territory at 21UTC, moving rapidly to the southeast, reaching the region of Lisbon around 00UTC on the 11th and the Algarve at 03UTC.
The Arouca Radar image (Figure 2a) shows the location of the cold front at 23:50 UTC - an organized line stretching from the region of Lisbon to Castelo Branco.
Figure 2b shows rainfall accumulated in 6 h (between 21UTC on December 10th to 03UTC on December 11th). It is verified that the greatest amounts of accumulated rainfall in six hours were located in the regions north of Coimbra and in Alto Alentejo, with values between 20 and 40mm.
The meteorological station network detected the intensification of the wind speed and heavy rain from the afternoon on 10th onwards.
Below the maximum precipitation values accumulated in 1h, 3h, 6h and 24h at IPMA Weather Stations Network.
Maxima Rainfall Accumulated (mm) 10/12/17:
Weather station - Arouca (1H) - 22.1
Weather station - V. N. Cerveira (3h) - 43.9
Weather station - Luzim (6h) - 73.1
Weather station - Cabril (24h) - 145.3
The highest values of average wind were recorded in the highlands and the west coast, where they were over 60 km/h. The highest values of the gust was also reached in these regions, with values exceeding 110 km/h in several places, namely: Mogadouro 129,2km/h, Guarda 129 km/h, Penhas Douradas 121 km/h , Moimenta da Beira 119.5 km/h, Cabo Carvoeiro 112.3 km/h, Fóia 105.1 km/h and maximum value 144, 4 km/h in Cabo da Roca.
Imagens associadas
Figure 1 – Storm Ana. Air mass RGB image (a) 10th December 2017 at 18UTC, (b) 11 th December 2017 at 00UTC, (c) forecast H + 6 of the ECMWF model from 10th December 2017 at 12UTC, mean sea level pressure (black lines, 4 in 4 hPa), wind direction and speed (barbs, knot), cold frontal (dark blue line), (d) Analysis of the ECMWF model from 11th December 2017 at 00UTC, mean sea level pressure (black lines, 4 in 4 hPa), wind direction and speed (barbs, knot), cold frontal (dark blue line).
Figure 2- (a) Maximum Reflectivity Product (dBZ) from December 10, 2017 at 23:50UTC, (b) Accumulated rainfall in 6 h (mm) between 21UTC on December 10th and 03UTC of 11th December 2017 (Arouca Radar).
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