Ag Weather Forum

The tropical season may be slow in terms of number of storms so far, but the ones that have developed have had an impact. Only seven storms have been named, but three have moved through the mainland United States while another tropical low that was never named moved into the Mid-Atlantic last week. Now, another tropical cyclone is developing in the northwestern Caribbean Sea and could rapidly intensify during the next couple of days.

Models have been eyeing this storm for about a week and been persistent in some sort of tropical cyclone for the Gulf of Mexico. During the weekend, they narrowed their focus on the eastern Gulf of Mexico and have been very strongly consistent both within their own envelope of runs, and between the models themselves.

A disturbance, which has been labelled as Potential Tropical Cyclone Nine by the National Hurricane Center (NHC), is developing in the northwestern Caribbean Monday and is forecast to pass into the Gulf of Mexico via the Yucatan Channel Tuesday night or early Wednesday, making landfall on the Florida Peninsula around Apalachicola on Thursday afternoon and evening.

The track and timing of this feature has been remarkably consistent. Models are also forecasting the storm to rapidly intensify. With the bathwater temperatures in the region of 28-31 degrees Celsius (82 to 88 Fahrenheit), any storm center should quickly use up the energy to strengthen.

The NHC has this cyclone becoming a hurricane before reaching the Gulf of Mexico and potentially becoming a Category 3, major hurricane, before landfall in Florida. A major hurricane is a Category 3 or higher cyclone with maximum sustained winds of at least 111 mph. The storm will be named Helene upon reaching tropical storm status with a clearly defined low-pressure center and maximum sustained winds of at least 35 mph.

Where it goes after landfall is a little more uncertain. An upper-level low is going to be cut off from the jet stream as it dives into the South-Central U.S. early this week as a strong ridge develops over the top of it in central Canada. That will help to guide the hurricane northward, but prevent it from moving too far north. However, the two low centers will be in close proximity and will likely interact with each other. Models sometimes do not do a good job of simulating this interaction, which may lead to significant consequences for those in the area -- especially when small changes in the exact location of the upper low, hurricane, northern ridge, and timing could play significant roles in the interaction.

In all likelihood, the two storm centers will sort of rotate around each other. The upper low being larger and more dominant will be less likely to move, but should pull the hurricane's remnant low northwest into the Tennessee Valley on Friday. Being cut off from the jet stream by the Canadian ridge, the two lows should move around the Southern U.S. through the weekend and likely a good portion of next week too. Any changes to the strength or location of the ridge axis, the upper low, or the eventual hurricane may cause major changes to the forecast for the interior U.S.

That complicates the rainfall forecast. How these storms interact will determine which areas see the heaviest rain and which others only see sporadic showers. No doubt the area around landfall, currently forecast to be the Florida Panhandle, eastern Alabama, and Georgia, should see the greatest rainfall amounts, which may lead to significant flooding, but also help with the growing drought in the region. But does the heavy rain back its way into Missouri? Or even Oklahoma? Does rain get spread northward through the Midwest in a significant way? All these questions are to be answered by how these two pieces of energy circle around each other and how long it takes to get a system to sweep it out. That is currently forecast to occur around the middle of next week.

The impacts from the storm could therefore be greater than just at landfall. Heavy rain is both a positive and a negative this time of year. On the positive side, the rain will help with the growing drought in the region and boost river levels. On the negative side, heavy rain can cause flood damage and bring delays to harvest and reduce quality of crops remaining in fields.

The NHC reminds people that without a clearly defined center yet developed, models have lower accuracy. But with all the global and regional models inferring the same idea on the track and timing of the system, there is high confidence in a landfalling hurricane this week in the eastern Gulf of Mexico, likely in the Florida Panhandle and possibly as a major hurricane. Heavy rain should move into the Southeast U.S. and could overspread a large portion of the southeastern quadrant of the U.S. and some more limited areas elsewhere.

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John Baranick can be reached at john.baranick@dtn.com

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