Extra Tropical Transition

General information: 6 August 2005 0600 UTC
By late on 5 August Alex had moved north of the Gulf Stream over sub-20°C waters and was weakening rapidly.

Moving at 40-45 KT, Alex weakened to a tropical storm after 0600 UTC 6 August and became extra tropical a few hours later about 830 NM east of Cape Race Newfoundland.

300 hPa contours
The zonal flow over the Atlantic has begun to intensify. The confluent upper trough has slowly relaxed to the northwest of the United Kingdom.

300 hPa winds
The jet core to the north of the now extra tropical storm has extended with the central core speed of between 95 and 120 KT. The jet core is also visible on the water vapour images and shows some darkening, which implies some acceleration.

300 hPa isotachs
The jet core to the north of the now extra tropical storm has extended with the central core speed of between 95 and 120 KT. The jet core is also visible on the water vapour images and shows some darkening, which implies some acceleration.

500 hPa contours
Zonal flow covers the Atlantic. A cut off mature upper low is evident to the North West of the United Kingdom.

Thickness
At this stage we see that the thickness values over the western Atlantic have risen significantly. We do however see that the amount of warm advection taking place ahead of the system has now greatly decreased as the thermal wind is generally align with the flow.

850θw
High Theta w values continue to advect eastwards.

The weak baroclinic zone extending from 50 °N 20 °W to 60 °N 60 °W is still a significant feature, however on the Satellite imagery this appears to be warming out and decaying.

Water Vapour 6.2µm
The jet is evident to the north of Alex, the PV maximum lies to the north of Alex. At this time Alex remains parallel to the Jet core and is not in the development region of the jet. The jet core has become even more elongated. The cloudiness to the southeast of Alex is within the zone of high humidity air which is decaying due to the influence of the right exit regoin of the jet stream.

Water Vapour 7.3µm
The jet is evident to the north of Alex, the PV maximum lies to the north of Alex. At this time Alex remains parallel to the Jet core and is not in the development region of the jet. The jet core has become even more elongated. The cloudiness to the southeast of Alex is within the zone of high humidity air which is decaying due to the influence of the right exit region of the jet stream.

PV at 300 hPa
The jet to the north of Alex is continuing to extend along with the PV maximum on the cold side of the jet. PV areaassociated with Alex has becominf elongated and is coinicident with a slight darkening zone, seen more clearly in the 6.2&micr;m WV channel. This PV area marks an area of slight troughing behind the hurricane and roughly marks the track of Alex.