Tropical Storm Karen has formed in the southern Gulf of Mexico from a disturbance that moved out of the Caribbean. Thunderstorm activity remains limited to the eastern side, and the circulation appears to be tilted to the east with height due to some southwesterly wind shear. Such shear is typical with October storms in the gulf, and it is unlikely to go away. In fact, as an upper trough digs in from the west as Karen nears landfall, this wind shear should get worse. Thus, the storm is likely to remain eastern-weighted, with most weather impacts occurring east of landfall in 60-72 hours. The NHC has increased Karen’s winds to 65mph after recon data during the night, but the thunderstorm activity has weakened since that time, and a new plane will re-assess Karen’s intensity. The maximum winds were very localized already, and with a central pressure of only 1005mb, Karen in reality is a pretty weak tropical storm at this time.
The GFS has been throwing a fly into the ointment by forecasting Karen to strengthen substantially before landfall, reaching minimal hurricane strength, along with a track farther east well into Florida. The GFS so far is the only global model to do this, as the ECMWF, UKMET, and CMC are not as bullish. I consider the GFS solution to likely be erroneous feedback, given that Karen is already struggling to get vertically stacked, and wind shear will only get worse with time. In addition, the low-level inflow pattern currently in place with large-scale anticyclonic (clockwise) flow in the SW Atlantic is not conducive for storms, as Karen will lose her moist inflow channel from the Caribbean as she moves north. The environment favors the ECMWF/UKMET/CMC solutions of a weak-moderate tropical storm moving into the north gulf coast, farther west than the GFS ahead of a mid-latitude trough. The NHC is forecasting Karen to become a hurricane and then weaken slightly before landfall, likely due to her initial intensity already being 65mph. Karen currently appears to be weaker, and if the next recon plane affirms this, then Karen’s chances of becoming a hurricane currently seem dim. Blustery, tropical storm force conditions and heavy rain will impact the north gulf coast east of the center at landfall late Saturday and Sunday.
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