The reservoirs of southern Spain have been severely depleted after many months of inadequate rainfall, so any rain that falls during May is very welcomed. This rain is normally the last useful replenishment before the hotels on the Costa del Sol fill with tourists, and the precious water is lost to the drains and sewers. The background for the Costa del Sol The average rainfall in May along the Costa del Sol is about 20-30 mm (0.8 to 1.2 inches), although there are wide variations due to the differing topography of the area. There are also large variations from year to year. For example, in both May 1997 and May 1998 Malaga Airport had over 40 mm (1.6 inches) of rain, but in May during the following year it only rained once with a total fall of less than 0.5 mm (0.02 inches). In April this year (2006), there was only about 50% of the average rainfall of around 40 mm (1.6 inches), and this came after a winter when precipitation was also well below normal.
Well telegraphed for Andalucia Towards the end of April, medium-range forecast charts were in widespread agreement that an unsettled spell of weather would develop in Spain, particularly the south, with the prospect of heavy rain over a large area. Surprising consistency in the forecast continued through into early May and by the late afternoon of 2nd the upper-air pattern was becoming conducive for widespread ascent and the resulting development of cumulonimbus clouds.
Setting the Scene During the day on the 2nd, it was very warm over most of Iberia with the satellite picture (Figure 1) suggesting plenty of sunshine (black areas), broken shallow cumulus and stratocumulus (dark grey areas) and mainly dense cirrus (white areas) over southern parts of both Portugal and Spain. Over the Sahara Desert there were large areas of dense cirrus in association with the subtropical jet, but across Morocco, to the west of the Atlas Mountains, there were lower clouds trapped under a marked inversion, the result of relatively cold low-level air spreading east from the cool eastern Atlantic Ocean. Under this canopy of low cloud, maximum afternoon temperatures were only around 18 or 19 Celsius (64-66F), but on the Costa del Sol, maxima were 21 to 23 Celsius (70-73F) despite an onshore sea breeze; and inland it was very warm with 29.5 Celsius (85F) at Sevilla, 30.0 Celsius (86F) at Cordoba, and 31.0 Celsius (88F) at Granada.
As the afternoon progressed, a shallow vortex, associated with the ragged cloud in Figure 1. between the Canaries and southern Portugal, drifted slowly east-northeast towards the Moroccan coast. Meanwhile, the lines of cloud to the northwest of Spain, continued to move eastwards. These latter clouds were part of an eastward-moving north Atlantic weather system and marked the forward side of an advancing upper trough.
The Thunderstorms develop During the evening, several factors contributed to thunderstorms breaking out. Firstly a series of medium-level storms developed over Morocco, ahead of the advancing upper vortex and aided by uplift on the approach to the Atlas Mountains, and secondly, straightforward cumulonimbus development occurred over southern Spain due to heating, the introduction of moister air at low levels due to sea breeze encroachment inland, and, more importantly, the introduction of moister air at medium and upper levels as the complex troughing over the Atlantic moved eastwards.
Figure 2 illustrates the emerging broad upper trough with noticeable advection and expansion east -northeastwards of the cloud mass north of the Canaries, and the thunderstorms (clusters of white clouds) particularly over Morocco, but also over southern Spain.
Figure 1. IR Satellite image 1200 UTC 2nd May.
Figure 2. IR Satellite image 1800 UTC 2nd May
The rapid development, and expansion, of thunderstorms is apparent on the evening of the 2nd when comparing Figures 2 and 3; and it was during this period that the most destructive storms occurred.
copyright 2006 EUMETSAT Figure 3. IR Satellite image 0000 UTC 3rd May
copyright 2006 EUMETSAT Figure 4. IR Satellite image 0300 UTC 3rd May
copyright 2006 EUMETSAT Figure 5. IR Satellite image 0600 UTC 3rd May
copyright 2006 EUMETSAT Figure 6. IR Satellite image 0900 UTC 3rd May
The evening of the 2nd As dusk approached, rows of huge towering castellated altocumulus clouds appeared in the haze south of Malaga and spread steadily northeastwards with ominously quick upward growth and lateral development. These clouds acted as fuel for the cumulonimbi that had already formed north of the mountains behind the Costa del Sol (see Figure 2) and the result was torrential rain and severe flash flooding. The worst affected area appeared to be north of Antequera and east towards Granada.
Figure 7. Map of the area affected by the flash flooding on the evening of 2nd May. The blue spot is near Cuevas Bajas and the green spot is near Loja
Countless streams and small rivers burst their banks. Crops to the value of 1.5 million euros were lost and the ground floor of many low-lying houses were inundated. The area around Cuevas Bajas (Figure 7) was particularly badly hit and the main road from Malaga to Cordoba was closed for several hours due to flooding. Around Loja (Figure 7), the main road to Granada was also closed due to flooding and 5 motorists had to be rescued. Many drivers had to spend the night in their cars as minor roads also became impassable. In all, 47 motorists had to be rescued from 25 vehicles across the provinces of Malaga, Granada and Murcia. Fortunately, there were no fatalities, but the clearing up operation for many families will undoubtedly last several months.
The Violent Weather At the peak of the storms, from late evening on the 2nd to the early hours of the 3rd , rainfall rates were exceeding 80mm(3.2 inches) per hour. Near Loja, there were over 40 mm (1.6 inches), most of which fell in just half an hour around 1 am. The worst of the rain, as is often the case, missed the rain gauges, but it is probable that falls of over 50 mm (2 inches) occurred and maybe locally 75-100 mm (3-4 inches). Although the area focused on was the area between Antequera and Granada, there was intense thunder and lightning on the coast between Nerja and Motril, as well as very gusty winds in the storms close to Almeria.
The worst was over It can be seen from comparing Figures 3 and 4 that the sharp difference between the white cumulonimbus clouds and the grey/black of cloud-free areas was beginning to blur by 0300 UTC. Of course, some of this can be explained by nocturnal cooling, but a glance at Figures 5 and 6 shows a further dissipation of the most vigorous convection. By the morning of the 3rd (Figure 6) , the rain was lighter, less thundery and, for southern Spain, largely associated with the shallow upper vortex which had now drifted northeast to be positioned southeast of Madrid.
Over the following 9 hours the upper low began to accelerate eastwards but skies stayed largely cloudy across Spain with further rain from time to time. Much of the rain was light but some thunderstorms developed (the whitest clumps of cloud on Figures 8 and 9), but generally they were less intense than on the previous evening and night. By the evening of the 4th, the thickest cloud and rain was becoming confined to eastern Spain (Figure 11.), with clear skies and the promise of sunshine returning to the Costa del Sol.
copyright 2006 EUMETSAT Figure 8 Satellite image 1200 UTC 3rd May
copyright 2006 EUMETSAT Figure 9 Satellite image 1800 UTC 3rd May
copyright 2006 EUMETSAT Figure 10 Satellite image 0600 UTC 4th May
copyright 2006 EUMETSAT Figure 11 Satellite image 1800 UTC 4th May
The Final Score In the table below are some of the rainfall totals that occurred from 1800 UTC on the 2nd to 1800 UTC on the 4th (25.4mm=1inch). Average May rainfall in brackets (where available).
Place Name
18-06 (2nd/3rd)
06-18(3rd)
18-06(3rd/4th)
06-18(4th)
=Total
Meknes (MA)
18
2
2
0
22
Fez (MA)
25
3
3
0
31
Malaga
9
0.2
2
0.1
11.3(20)
Granada
17
2
0.2
0.2
19.4(28)
Sevilla
8
2
6
0
16 (34)
Cordoba
6
11
6
0
23 (34)
Almeria
6
1
9
0.5
16.5(14)
Murcia/S. Javier
n/a
Tr
Tr
7
n/a (31)
Jerez de La F
6
0
2
0
8 (37)
Murcia
16
Tr
0.1
Tr
16.1(32)
Gibraltar
0.6
0
0
0
0.6 (27)
Faro
0
0
0
0
0 (27)
Murcia/Alcan'
17
Tr
0.1
0.5
17.6(32)
Moron de La F
28
0.2
6
Tr
34.2
Madrid
0
0.8
2
2
4.8 (47)
Alicante
2
0
Tr
Tr
2 (33)
Valencia
0.3
10
Tr
Tr
10.3(34)
Ibiza
0.8
3
0
9
12.8(26)
Palma
0
Tr
0
2
2 (27)
Mahon(Men'a)
0
0
0
0.5
0.5 (37)
Barcelona
0
Tr
0
0
Tr (59)
Oviedo
0
2
10
1
13
Santander
0.4
0.4
0
7
7.8 (89)
Jaen
6
6
3
0.2
15.2
Copyright Malaga Weather Channel 2006
User comments
Peter latham Excellent website, not too technical and well illustrated.
All pages well laid out.
