Storm Forecast
Valid: Tue 08 Nov 2011 06:00 to Wed 09 Nov 2011 06:00 UTC
Issued: Tue 08 Nov 2011 00:42
Forecaster: TUSCHY

A level 1 was issued for parts of the W-Mediterranean mainly for heavy rainfall and gusty winds.

A level 1 was issued for Sicily, S-Italy and the N-Ionian Sea mainly for large hail and strong to severe wind gusts.

A level 1 was issued for Albania mainly for heavy rainfall.

A level 1 was issued for parts of Portugal mainly for an isolated tornado event, marginal hail and strong wind gusts.

SYNOPSIS

No major changes in the synoptic pattern analysis. Still major high-over-low blocking pattern present over Europe with cold conditions over far E-Europe. Hence any thunderstorm activity remains confined to the western/central Mediterranean.

A side-note:

****** Tropical storm 01M/99L ******

SUMMARY: 9th NOV. 2011, 0000 UTC
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LOCATION...42.6N 6.4E
ABOUT 61 NM...112 KM SE OF MARSEILLE
ABOUT 111 NM...205 KM WNW OF AJACCIO, CORSICA
MAXIMUM SUSTAINED WINDS...52 MPH...83 KM/H
PRESENT MOVEMENT...QUASI-STATIONARY
MINIMUM CENTRAL PRESSURE... Between 1005 and 1009 hPa

UPDATE 00 UTC, 9th Nov.: Surface data indicates that the persistent outer band in the NE quadrant of "01M/99L" may have been able to mix down stronger winds than previously anticipated with Porquerolles reporting steady winds of 27 m/s and gusts of 42 m/s. With more coastal stations showing steady winds only marginally weaker, "01M/99L" may have peaked in intensity this afternoon/evening as a strong tropical-like cyclone (we're not sure if indeed true tropical warm-core characteristica were present during that time with a vertically tilted/sheared core, a more asymmetric wind field and absence of DMC next to the center for a couple of hours). Since then, the convection weakened significantly but a 23 UTC ASCAT still indicates winds around 40 kt (75 km/h). Hence, the current intensity rating still exceeds the latest Dvorak classification. Banding structure remains good and pulsating convective re-development next to the center is still possible during the rest of the outlook. Excessive rainfall and severe wind gusts continue to affect the coast of S-France during the following hours although some weakening may occur as a consequence of weakening DMC. There is no major change regarding path and intensity forecast compared to the 18 UTC update and hence this will be the last regular update. More informations will become available in the next Severe Weather Outlook Day 1. If any unexpected intensification occurs, another update will be issued. Otherwise, we will now return to the regular outlook style.

UPDATE 18 UTC: Both shear and dry air seem to have taken their toll on 01M/99L. Latest HVIS data indicated a tilted vortex with the LLCC somewhat displaced to the SW (probably forced by modest NW/W-erly shear at higher levels). Current thinking is that if any warm-core structure is present, it will be a tilted one. Nevertheless, latest SAB update indicated another increase in strength and latest ASCAT data reveals 40-45 kt in the northern quadrant (some arrows not contaminated by ongoing DMC). The question arises, if this is not more typical for a subtropical feature due to ongoing modest shear. The system also has looped during the past few hours with only marginal movement to the north. A band of intense convection affects parts of SE-France right now and heavy to isolated excessive rainfall will be an imminent risk, next to an isolated tornado event with augmented LL shear! Further bands with heavy rainfall may affect SE-France/W-Ligurian coast during the night as the cyclone remains just offshore. Future intensity signals are mixed for 01M, as shear abates somewhat but it remains atop marginal cooler SSTs and it has drier air to the west to work with. Soundings upstream also confirm a slow warming trend at mid-levels. We would not be surprised to see a more pulsating activity of DMC next to the center/along the bands during the next 12-24h, but overall signs are more against another intense flare-up of persistent DMC. Models still show a stalling or westward moving system while weakening ahead of another upper trough over the far W-Atlantic.

UPDATE 12UTC: The new update of SAB now indicates some weakening, as deep convection failed to re-develop mainly in the western part. WV imagery also indicates some dry air intrusion from higher levels, which gradually raises concern about how pronounced the warm core structure is right now. However, intense DMC evolved in the last hour or so mainly in the eastern/northern part and starts to wrap around the center. UW CIMMS also hints on somewhat augmented shear, which should remain steady during the next few hours. The cyclone now starts to increase its forward speed and moves more to the ENE to NE. This may be the result of an upper wave, which passes by to the west. Models want to stall this feature just SW of Liguria as the upper waves moves off to the north later tonight. The risk for strong downpours and gusty winds may increases over far SE France and probably along the W-Ligurian coast during the following hours.

UPDATE 06UTC: The center of the cyclone again became better organized with the strongest convection now in the southern and eastern part (maybe enhanced by the jet streak, which passes by to the SE). Some slow movement to the east occurred but despite a further consolidating cyclone, latest reports do not indicate any strengthening (also assisted by ASCAT data). No further surface reports were available.

NOTE 1: Despite issuing new ESTOFEX updates, this part of the outlook will be updated when new informations become available. Please check this table for further updates during the upcoming 24 hours.

NOTE 2: ESTOFEX is not responsible for forecasting any tropical storm activity. This is just an additional information and therefore captured as a "side-note". For more informations, please contact the following address of the Satellite Analysis Branch (http://www.ssd.noaa.gov/PS/TROP/2011/bulletins/archive.html,[SAB]).

As of 18 UTC (7th Nov.), the Satellite Analysis Branch upgraded the depression over the W-Mediterranean to "Tropical system 01M", as convection persisted for an adequate time atop the center. Since then, deep convection weakened somewhat with warming cloud tops next to the center. Nevertheless, very good banding is now present in all quadrants with good outflow atop (especially to the NE, pointing to a 30 m/s 300 hPa jet). A Dvorak number-pressure relation was used for the pressure classification (also at 21Z at the 7th, a ship at position N 41°36' , E 6°06' reported a pressure of 1005.0 mb with 38kt winds from 160°). The final wind strength reflects the intensity of the latest SAB guidance.

There remains some time left for further intensification, before geopotential heights slowly increase during the end of the forecast period. We would not be surprised to see another flare-up of DMC along the center due to the convective cycle of those features (peaking during the morning hours). The N-outflow may weaken somewhat as the upper jet to the north weakens, but at the same time the southern outflow channel could take profit of a 300 hPa streak, which crosses Sicily during the forecast from SW to NE. SSTs remain at or above 20°C, whereas 500 hPa temperatures gradually warm up 1-2K until 06Z. Combining all those effects, some further organization/strengthening is forecast if this system can support more convective bursts along the center before overall conditions become somewhat less favorable during the night hours onwards.

The storm motion is handeled badly by the models...without surprise. 01M is captured in a very weak steering flow and most models now show a system, which meanders around between the Balearic Islands and Corsica/Sardinia. In any case, residents along the adjacent coasts should keep a close eye on the further development of this feature as bands of strong convection may bring heavy downpours next to gusty winds.

A level 1 was issued not for the system itself (as we do not forecast tropical cyclone activity), but for the showers/thunderstorms, which accompany that cyclone. The level 1 covers heavy rainfall and strong to isolated severe wind gusts.

DISCUSSION

... Sicily, Ionian Sea and S-Italy ...

A 25 m/s mid-level streak enters the area of interest from the SW during the start of the forecast and shifts to the NE while weakening. This causes a rapid increase of the 0-6km bulk shear to the order of 20 m/s and more. An overlap of 500-800 J/kg MLCAPE and aforementioned shear assist in a sector, where organized multicells/isolated supercells are possible. Large hail and strong to isolated severe wind gusts will be the main hazard with those storms. The set-up supports the development of a cluster of showers/thunderstorms over S-Italy/N-Ionian Sea, which may affect parts of Albania with heavy rainfall during the night. Hence the level 1 was expanded well to the east.

... Parts of Portugal ...

A frontal boundary is forecast to affect far W-Portugal after 00Z onwards. A plume of subtropical air is advected towards Portugal ahead of this front as sampled by latest MIMIC-TPW data. As mid-levels start to cool down atop that moisture tongue, instability increases with 500-800 J/kg MLCAPE forecast. At the same time, a surface trough strengthens just west of Portugal and assists in a backing wind field. This results in augmented directional shear (combined with ageostrophic deflection onshore) and hence thunderstorms may gain some organization. There still exist uncertainties how fast the front will move onshore, but current thinking is that at least a few storms occur before 06Z. Marginal hail and strong wind gusts accompany those storms. An isolated tornado event along the coast is possible.