At 12Z on July 11th, there was ridge centered
near Arizona, an anti-cyclone over the eastern Gulf of Mexico, and a trough over
the Great Lakes region. Weakening of a mid/upper-level ridge along the northern
Gulf coast was caused by the Great Lakes trough, as a vortmax came down over the
upper Midwest, reinforcing the trough. The weakening of this ridge allowed for a
more northward turn for Claudette.
Though there was a strong break in the ridge at this time, the anti-cyclone over
the eastern Gulf of Mexico was building westward, closing this break and
allowing Claudette to turn back westward. This ridge to the north of the storm
was a source of forecast uncertainty. If the ridge is weak, the storm will go
northward, but would go more westward if this feature was stronger.
The ET KF targeting map valid for taking observations on the 12th at 00Z to
improve forecasts on the 14th at 00Z indicates that observations should be taken
near and to the north-east of the storm. These observations would improve the
analysis of Claudette, the asymmetry of Claudette, as well as interactions
between Claudette and the anti-cyclone in the eastern Gulf of Mexico. A second
area for observation is in Mexico, associated with the broad cyclonic flow
around tropical storm Enrique. As Enrique was moving away from Claudette, and
dissipating, it was the break in the ridge which was most important to the path
of Claudette.
The flight sampled most of the Gulf of Mexico, roughly circling Claudette.
At 12Z in the 13th, there was still a ridge
centered in Arizona, and the trough over the central United States. The ridge
over the western United States became a more dominant weather feature, and
helped push Claudette to the west. At this time, the trough axis was past
Claudette, but another vortmax was coming down from the Midwest that would
deepen the trough and turn Claudette more to the north.
The ET KF targeting map valid for taking observations on the 14th at 00Z to
improve forecasts on the 16th at 00Z indicates that observations should be taken
near and to the south-east of the storm. These observations would improve the
analysis of Claudette, the asymmetry of Claudette. The ET KF indicates that
areas to the west of Claudette (over Mexico) to the North-West of Claudette
(over Texas) and to the North-East of Claudette (Florida Panhandle) are also
areas where observations would improve the future forecast of Claudette. As all
of these areas were over land, they were inappropriate locations for dropsonde
observations. It is primarily in and to the east of Claudette that observations
should be taken. Observations to the east of Claudette will again help to
ascertain the intensity of the anti-cyclone to the east of Claudette.
Again, the recon flight sampled the atmosphere over the Gulf of Mexico, roughly
encircling Claudette.
