Gustav is currently moving to the northwest as it has encountered a weakness in the ridge. A strong ridge is forecast to develop on Monday that will turn Gustav more to the left. Just how much to the left has a large impact on exactly where Gustav will make landfall. There is decent model agreement that the ridge will not be strong enough and will cause Gustav to make landfall in Southern Louisiana. I'm still remaining firm in my forecast that the ridge will be stronger than models suggest and will cause Gustav to make landfall near Sabine Pass, TX.
The intensity at landfall is quite problematic at this time. Before that, it still appears that Gustav will probably acquire Category 5 status at some point in the Gulf of Mexico. I don't think it will be able to maintain that intensity all the way to the coast, but the 06Z GFDL suggests it is certainly possible. Let's hope that particular run is not correct! However, water temperatures are still plenty warm near the coast (86 - 89 F) to support a Category 4 or 5 hurricane.
Caution should be used when looking at the Tropical Cyclone Heat Potential product and just assuming that it is not high enough near the coast to support a Category 4 or 5 hurricane. Remember that it is an integration from the top of the sea surface to the depth of the 26 degree Celsius isotherm. The continental shelf off the northern Gulf Coast is extremely shallow and is too shallow to give an accurate measure of TCHP.
Regardless, wind shear is forecast to increase as Gustav approaches the coast and this will certainly limit strengthening and probably cause it to weaken. Another possibility is that Gustav could entrain some dry air as it gets closer to the coast which would certainly act to weaken the system. It's too early to say whether that will happen at this time. In addition to environmental factors affecting intensity, eye wall replacement cycles will also dictate the strength of Gustav. If it is undergoing an eye wall replacement cycle, it will probably be in a weakening trend. These cycles typically take about 24 hours to complete. However, if Gustav has completed an eye wall replacement cycle before landfall, it could actually be strengthening or maintaining its strength at landfall. Eye wall replacement cycles near the time of landfall are impossible to forecast at this time. Conditions are expected to be supportive of at least a Category 3 hurricane at landfall, but I'm still forecasting Gustav to be a weak Category 4 hurricane when it crosses the coast.
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2 comments:
Eyewall replacement cycles are impossible...but an eye usually lasts somewhere between 12-36 hours. So lets say the eye clears out in the next few hours, and isn't disturbed by a short trip over Cuba...this would put an eyewall replacement just before it makes landfall...which would be ideal.
But lets say the eye is disturbed as it crosses Cuba...it redevelops over the loop current...and then it doesn't have time to go back into a cycle before landfall. But of course, this is all hypothetical. Hopefully that little bit of shear will weaken it before landfall anyway.
Yes, let's hope the shear and some dry air pummel it before landfall!
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