HURRICANE GORDON and the NWP models near the Iberian Peninsula

Are tropical storms so tropical? Extratropical transition: Many tropical hurricanes and storms, evolves, change and end their lives in non- tropical latitudes with non-tropical characteristics Extratropical transition: Many tropical hurricanes and storms, evolves, change and end their lives in non- tropical latitudes with non-tropical characteristics

Two more arrivals in 2005

Tropical vs. extratropical warm-core, symmetry warm-core, symmetry non-frontal synoptic-scale non-frontal synoptic-scale originating over tropical or subtropical waters originating over tropical or subtropical waters Once formed is maintained by the extraction of heat energy from the ocean at high temperature and heat export at the low temperatures of the upper troposphere Once formed is maintained by the extraction of heat energy from the ocean at high temperature and heat export at the low temperatures of the upper troposphere cold-core, asyimmetry cold-core, asyimmetry frontal synoptic scale frontal synoptic scale originating over middle- latitudes originating over middle- latitudes Once formed is maintained by the extraction of energy from the baroclinic effects Once formed is maintained by the extraction of energy from the baroclinic effects

Extratropical transition term used to indicate that a tropical cyclone has lost its "tropical" characteristics. term used to indicate that a tropical cyclone has lost its "tropical" characteristics. poleward displacement of the cyclone poleward displacement of the cyclone conversion of the cyclone's primary energy source from the release of latent heat of condensation to baroclinic processes. conversion of the cyclone's primary energy source from the release of latent heat of condensation to baroclinic processes. It is important to note that cyclones can become extratropical and still retain winds of hurricane (64 kts) or tropical storm (33 kts) force. It is important to note that cyclones can become extratropical and still retain winds of hurricane (64 kts) or tropical storm (33 kts) force.

Surface wind distribution Tropical and transition lows: an accurate track forecasting is important to get an accurate wind forecast Tropical and transition lows: an accurate track forecasting is important to get an accurate wind forecast

Extratropical transition Some environment changes: Increasing baroclinicity and wind shear Increasing baroclinicity and wind shear Lower SST Lower SST Intense SST gradient Intense SST gradient Upper level trough Upper level trough Humidity gradient Humidity gradient

Extratropical transition System transformations Intensity decreases Intensity decreases System velocity increases System velocity increases Loss of symmetry (winds, temperature, humidity, convection, cloudiness...) Loss of symmetry (winds, temperature, humidity, convection, cloudiness...) Loss of the warm core Loss of the warm core Possibly the system gets embedded in front or trough Possibly the system gets embedded in front or trough Possible deepening later (cyclogenesis) Possible deepening later (cyclogenesis)

September 2006: Hurricane Gordon It became Hurricane (64 kts) on 12 September Peak intensity (105 Kts) on 14 September Second peak intensity (90 Kts) on 19 September W of Azores Very fast movement Extratropical 00 UTC, 21 September New deepening 21, 22 September interacting with middle-latitude system

Hurricane Gordon -

Gordon: Extratropical transition Surface Pressure ECMWF Analysis

Gordon: Extratropical transition

Gordon: winds at coastal stations

Gordon: Effects on land Sustained winds of 100 km/h, gusts of 170 km/h Sustained winds of 100 km/h, gusts of 170 km/h 4 people injured (1 killed in Oporto?) 4 people injured (1 killed in Oporto?) Power outage affecting thousands Power outage affecting thousands Roofs and trees destroyed Roofs and trees destroyed No heavy rainfall No heavy rainfall

What did the models predict just 24 hours before the arrival to the Iberian Peninsula? Forecaster’s shift: early morning, 20 September when Gordon near Azores (red arrow) We’ll examine the data at that moment and the forecasts by diferent models focusing mainly on track, timing and depth (wind force) Forecast time will be 24 hours, between 06 UTC and 12 UTC, 21 September (green arrow)

Synoptic conditions at 06 UTC, 20 th September

ECMWF surface pressure: run 12 UTC, 19th September H H+48 Good track forecast Good track forecast Centre pressure too low (970 hPa) Centre pressure too low (970 hPa)

INM HIRLAM forecasts: run 00 UTC, 20 th September H H+36 There is no a distinct low pressure center useful in forecasting

Forecasted winds 06 UTC, 21 th September ECMWF INM HIRLAM Both models represent the convergence line ECMWF shows an evident cyclonic feature HIRLAM shows little evidence of Gordon The fast movement of the cyclon causes the deformation of the wind field around it

HELKI HIRLAM forecasts: run 00 UTC, 20 th September H H+36 Gordon erroneously landfalls At 12 UTC is leaving the coast moving northward (bad timing) Centre pressure too high (990 hPa)

ECMWF EPS run 12 UTC, 19 th September The area with the highest probability is on land and includes control Operational model differs greatly from control

National Hurricane Center U.S.   Forecast disseminated at 21 UTC, 19 September   The track (black line) is decided by the forecaster   It seems that Gordon landfalls at 07 UTC, 21 September

Multimodel Multiboundary SREPS High values of spread around the position of Gordon High values of spread around the position of Gordon

SUMMARIZING Track forecasting: will GORDON landfall? NO Operational ECMWF and EPS (low probability) YES HIRLAM, NHC and EPS (higher probability) Intensity forecasting: central pressure (hPA) at 06 UTC, 21 September: Analyzed value: 980 hPa ECMWFHIRLAMNHC

Conclusions: Gordon was a very fast moving structure Gordon was a very fast moving structure Intensified rapidly as extratropical low Intensified rapidly as extratropical low It had low predictability, even in the short range It had low predictability, even in the short range A real time vigilance is especially needed in these cases A real time vigilance is especially needed in these cases

Thank you for your attention