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Storm Forecast
Valid: Sat 13 Oct 2018 06:00 to Sun 14 Oct 2018 06:00 UTC
Issued: Fri 12 Oct 2018 23:45
Forecaster: BEYER
A level 3 was issued for parts of Portugal surrounded by a level 2 covering also parts of Spain mainly for severe to damaging wind gusts and to a lesser extent for (strong) tornados and excessive precipitation.
A level 2 was issued for parts of Sicily and Malta for excessive precipitation.
A level 1 was issued for parts of Turkey and Cyprus for excessive precipitation.
SYNOPSIS
A strong and widespread upper level high is influencing large parts of the forecast domain with stable conditions. South of the high-pressure system two separated upper-level lows can be found over the Mediterranean Sea - one close to Turkey and the other over Southern Italy and Sicily.
Over the near North Atlantic Ocean, a strongly amplified and broad trough is active, leading to that southerly /southwesterly flow over most parts of Europe and thus to unusually warm temperatures over most parts of Europe. On the forward flank of the trough, several surface lows have traveled northeastward brought mostly non-convective severe wind gusts to parts of the British Isles. On Saturday another low is influencing that area that however is much weaker.
The most interest on that day is hurricane Leslie that is quickly traveling eastward and will probably reach the Iberian Peninsula during the night from Saturday to Sunday posing a high risk for severe and damaging wind gusts.
DISCUSSION
...Iberian Peninsula...
Hurricane Leslie is rapidly approaching Portugal and will likely bring severe to damaging wind gusts during the night hours of Sunday
Looking at the current satellite images Leslie still looks well organized with a symmetric cloud shield and cloud top temperatures of almost -70 degree C. The central pressure is estimated to be around 971 hPa.
At the moment Leslie can be found to the south of the upper-level trough. It is forecasted that it should be taken up by the trough in the upcoming hours leading to a further acceleration of its movement to the east and also leading to a beginning transition into an extratropical system during the forecast period. However, models keep Leslie as a system with a tropical appearance for a long time when approaching the Iberian peninsula. It is also forecasted that the system should stay rather strong until it will make landfall. Although increasing shear and somewhat lower SSTs should normally weaken Leslie, the interaction with the through is probably the reason why its central pressure is forecasted to not rise significantly or even drop again during the night time.
The symmetrical appearance will probably disappear in the evening hours due to the aforementioned transition process. Models forecast the strongest pressure gradient to the south and to the west of Leslie. Together with the movement speed of Leslie, the regions of the southern flank of Leslie should see the strongest gusts but with that strong gradient west of the core, the whole coastline can be affected by severe wind gusts. Winds in 925 hPa are forecasted up to 50 m/s.
Ensemble forecasts show a significant probability of wind gusts in the excess of 30 m/s in the aforementioned area. Depending on the model damaging wind gust higher than 40 m/s are well possible. A few solutions also show more than 50 m/s. The risk of severe wind gusts can also affect parts of Western and Northwestern Spain although the storm is significantly weakening more inland.
There are still uncertainties in the exact track of Leslie and in the strength it makes landfall. ICON and ECMWF are the models that show Leslie making landfall at hurricane strength on a northerly course from Lisboa to northeastern Portugal. GFS, however, has a much weaker storm that is also moving on a more southerly track. However, models are getting more and more confident concerning a strong landfall.
The time of the landfall is expected to take place at around midnight (MESZ).
Although it is rather questionable if convections (in form of lightning) may develop we decided to issue an LVL3 area for the wind risk that comes from a convectively driven system that is only slowly transforming into a low with extratropical character.
Besides the wind risk, a locally excessive precipitation threat exists since the system brings a lot of liquid water. However, models do only give little hints for higher amounts of precipitation which is probably due to the rather fast movement of Leslie and the orography of the affected area. But amounts of 30 to 80 mm in a short time frame may lead to local flash floods.
Strong low-level shear together with low LCL would lead to an enhanced threat for tornados that may also be strong. This risk is highest to the south of Leslie where also notable CAPE values of a few hundred J/kg can be expected along a developing cold front. Also, a nice maximum of moisture convergence traveling eastward can be found in the models. This is the reason why the LVL2 area was extended to the south.
There will be an update on Leslie during the day.
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