On Monday afternoon, Francine spun above water, its temperature nearly ideal for a bathtub, primed to fuel, strengthen and sustain a hurricane.
With the storm becoming better solidified, a stronger hurricane than forecast, even a major hurricane — Category 3 or higher — is not out of the question.
That is to say that if conditions are close to perfect, a surprise rapid intensification is possible, said Brian McNoldy, an expert in hurricane formation and ocean temperatures at the University of Miami. He cautions that there are meteorological factors, like structure, land interaction and wind shear, that may work against its intensification.
As of Monday evening, Francine was a tropical storm in the western Gulf of Mexico and was expected to make landfall sometime Wednesday in Louisiana.
There is a short window between Monday afternoon and Tuesday night when rapid intensification of wind speeds by 35 miles per hour or more in 24 hours could occur. Even some of the forecast computer models have some outliers that show the intensity of Francine reaching Category 3 or 4. Dr. McNoldy said he “wouldn’t blindly dismiss high-end outliers in the Gulf of Mexico in the second week of September.”
The storm still needs time to consolidate and become symmetrical before it can intensify. And because it is only a little over 100 miles from land, the friction from the ground surface can also limit growth. If it can overcome those hurdles, Dr. McNoldy said, the ocean below it (meteorologically, the Gulf is the same as the ocean) is a huge fuel source to keep those thunderstorms going strong.
The level of energy in the waters of the Gulf of Mexico that is available to fuel a hurricane, as Dr. McNoldy said, continues to “obliterate” records that go back to 2012. The fuel, called the ocean’s heat content, describes the amount of thermal energy stored in the ocean — the higher the amount, the greater the influence it can have on storms like Francine.
The National Hurricane Center has hinted that rapid intensification might be possible, indicating in its 5 p.m. update on Monday that the tropical storm appeared poised to intensify more significantly in the short term. In a briefing this morning, a National Weather Service meteorologist in Lake Charles, La., said it is always best to prepare for a category stronger than the one being forecast — which, as of 5 p.m. Monday, was for a peak as a Category 2 hurricane.
The hesitation behind the forecast intensity has much to do with another weather pattern that will not only steer Francine toward the northeast but may also thwart its intensification.
On Wednesday, as the storm is expected to make landfall, it could collide with a cooler air mass that could cause the storm to reach a plateau in intensity or even to weaken as it comes ashore.
The faster that air mass approaches, the weaker the storm might be at landfall, and forecasters believe that the wind shear — when wind speed and direction vary with altitude — will increase in the final 12 to 18 hours before landfall, halting its intensification at a Category 2 hurricane.
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