Sunday, July 6, 2008
Daily Bertha Update
18z=2PM EDT
Since I wrote this discussion earlier in the day, I will update that microwave imagery shows a developing eye and improving inner core, and the IR/water vapor are also showing an eye trying to form, so I have upped the intensity forecast.
Discussion:
This afternoon Bertha may have re-formed a little farther northward under the deepest convection, and appears to be getting stronger. Now, for my path, I continued the general brisk WNW motion it is on now for the next couple days because there will be nothing to really change the direction of the storm, as it will continue tracking along the southern side of the mid-level ridge. However, late Tuesday a S/W will be moving well north of the system. It will weaken the ridge a little and may increase shear a little over the system Tuesday, so starting Tuesday I will show a slightly more north component in the path. On Thursday another S/W will move off the east coast. This will again weaken the ridge, and pull Bertha even more to the north. Now, there are a few questions here. Will the S/W be strong enough to wisp Bertha safely out to sea? Or will the ridge build back quick enough to trap Bertha just off the SE coast until the next S/W breaks down the ridge? The answers to these questions will depend on the strength of Bertha, the strength of the S/W, and the exact location of Bertha. A weaker Bertha would likely be trapped by the ridge building back, but a Bertha that is stronger and maybe a little farther NW would probably go out to sea without getting trapped by the ridge. But again, the answers to those questions are uncertain, so on my track I showed a slowing of Bertha towards the end of the week and a turn to the N. But again, after Wednesday things are a little uncertain. However, the threat to the US has gone down, because Bertha either goes out to sea safely, or if it does get trapped, which has a lower chance of happening there will be ridging off the SE coast and over the GOM, which should keep Bertha from drifting into the US. So, I will put the chances of Bertha hitting the US at 15%, and the chance of it impacting Bermuda at 50%.
For the intensity forecast, over the next couple days warmer SSTs and low shear should allow for a gradual strengthening. However, there will be a couple S/Ws tracking north of the storm (as mentioned above) after Tuesday, which will occasionally increase shear. While the current indications are the shear shouldn't tear Bertha apart, it may slow or even halt development.
18z Mon: 75-80MPH
18z Tue: 85-90MPH
18z Wed: 90-95MPH
18z Thu: 85-90MPH
18z Fri: 85-90MPH
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