Heavy precipitation in the Algarve - November 1, 2015
2015-11-04 (IPMA)
At 00 UTC of November 1, 2015 the weather was conditioned by a low with 1013 hPa centered in North Africa, in a deepening process and moving northwestwards, being at 12 UTC in the region of Faro with 1009 hPa and, at the end of the day, in the Atlantic southwest of Cabo Raso (38º N 10º W), with a minimum mean sea level pressure of 1005 hPa.
Associated with this depression organized lines of precipitation formed, with a Southeast- Northwest orientation, mainly affecting the western Algarve region in its northward trajectory between 4 and 14 UTC, with a particular focus on the area between Portimão and Faro, resulting in strong and persistent rainfall and in the developing of thunderstorms.
The Automatic Weather Stations (AWS) of IPMA´s network close to the most affected zone, recorded maximum rainfall of 11 mm in Portimão at 11 UTC and 20 mm in Faro-Airport at 12 UTC, with a maximum value in this last station of 74 mm in 6 hours (between 6 and 12UTC). The higher values of 1, 6 and 24 hour precipitation observed on November, 1 at AWS in the Algarve are shown in table 1.
As the precipitation lines progressed Northward, they gradually lost activity, coming to reach the other parts of the South and the Central region of Portugal mainland but already with much lower precipitation amounts.
The sequence of the images RAIN1 radar product (precipitation values in mm, estimated using the meteorological radar of Loulé/Cavalos do Caldeirão) obtained for the period between 10 and 14 UTC (figures 1 to 4) highlights the affected area, located between Portimão and Olhão. Considering the estimates obtained with radar for the period between 4 and 14 UTC, it is likely that the highest values observed in Faro and Portimão have been exceeded in the coastal area between Albufeira e Quarteira.
By applying adjustment factors Udometer-Radar obtained for the EMAs location of Faro-airport and Portimão, it is estimated that the value of precipitation between 4 and 14 UTC, in Albufeira and Quarteira, may have ranged values from 106 mm and 139 mm, with an estimated average value of 122 mm.
Table 2 shows the historical maximums of precipitation recorded at weather stations in the Algarve. The comparison of maximum values of precipitation with the ones observed on November 1, 2015 shows that:
- At Faro-Airport the historical hourly maximum is about 3.4 times higher than the one observed in this episode and the historical 6 and 12 hours maxima are about 1.5 times greater than the one observed;
- At Portimão the historical hourly and 6 hours maxima are about 2 times higher than those observed in this episode and the historical 12 hours maximum is about 1.3 times higher than the one observed.
Table 1 - Higher values recorded on November 1, 2015 of 1 hour, 6 hours and 12 hours precipitation at meteorological weather stations in the Algarve
Table 2 - Historical maximum values of 1hour, 6 hours and 24 hours precipitation (mm) at meteorological weather stations in the Algarve.
Figure 1 - Hourly rainfall values in mm (RAIN1 radar product), for the period 10-11 UTC
Figure 2 - Hourly rainfall values in mm (RAIN1 radar product), for the period 11-12 UTC
Figure 3 - Hourly rainfall values in mm (RAIN1 radar product), for the period 12-13 UTC
Figure 4 - Hourly rainfall values in mm (RAIN1 radar product), for the period 13-14 UTC
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