The strong trough of low pressure produced ice storms in Oklahoma and Texas on Tuesday and Wednesday while en route to the Gulf of Mexico. There, its high winds in the upper atmosphere were expected to shear Zeta's clouds and keep it at tropical storm or Category 1 status.
Instead, those winds helped draw warm air from the surface through Zeta's eye to its top, further reducing the storm’s central air pressure and helping it strengthen, senior hurricane specialist Mike Brennan said.
. . .
And as it neared Louisiana, Zeta’s forward speed increased, to almost 25 mph. That nixed another potential weakener: the cooler water along the state’s coastline. Had the storm been advancing at only 5 mph, it might have mixed cooler water from the Gulf’s depths to the surface, reducing the energy fuel that was keeping it strong, Brennan said.