There is great concern over a precipitation accumulation north of Venezuela dubbed “Invest 98L,” which has passed the Windward Islands with gale-force winds and rain. This one will remain tame until the weekend when it is ready to move into a powder room atmosphere. Next week, it could enter the Gulf of Mexico, although its exact path is still uncertain. Assuming it develops into at least a tropical storm, it will be named Hermine. The National Hurricane Center gives it a 90 percent chance of doing so. For now, anyone living along the Gulf Coast and Florida should pay close attention to this as the forecast evolves over the next few days. Fiona will hit parts of Canada as the region’s strongest storm on record At present, it is poorly organized. The reason it doesn’t do much yet is because of the disruptive shear, or change in wind speed and/or direction with height, that it faces. Excessive shear can whip up a new storm, as if undergoing a game of atmospheric tug-of-war. This shear originates from the high-altitude outflow, or evaporation, of Fiona far to the northeast. Invest 98L will meander west over the next few days, remaining a barrier to shear through Sunday. Things will escalate a lot fast Sunday afternoon to Monday. That’s when the shear will relax at the same time as 98L moves over some of the warmest waters in the Atlantic. The northwestern Caribbean is filled with ocean heat content, or thermal energy contained in bath-like ocean waters, which will support rapid consolidation and strengthening of the nascent storm. At the same time, 98 liters – by then probably a named storm – will move under an upper-level high-pressure system. This will work in the 98L’s favor in two ways:
Deviation. High pressure means the air is breaking apart. This divergence in the upper atmosphere will have a vacuum-like effect, creating a vacuum and facilitating the ascent of surface air. This strengthening of the storm’s updrafts will speed up how quickly the warm, moist “inflow” can enter the storm. Outflow. The high ones rotate clockwise. This is the direction of tropical cyclone outflow in the Northern Hemisphere. This high pressure will work with 98 liters to evacuate the “spent” air at high altitudes away from the storm, allowing it to swallow more air from below. Imagine placing an extractor fan at the top of a chimney. Air would be drawn up and out, meaning more air would enter from the bottom and the fire at the base would grow. This storm will do the same.
There is a chance that a very strong storm will be located somewhere in the northwestern Caribbean on Monday. It can escalate quickly at that point. However, it could follow anywhere from Mexico’s Yucatan Peninsula to central Cuba. But the storm could also slip between those areas, entering the Gulf of Mexico late Monday or Tuesday. There are only two escape routes that might allow the storm to avoid the gulf. There is an outside chance that, if it remains weak, it could continue westward in the Caribbean toward Central America. If it strengthens quickly, it could turn north over central Cuba and curve toward the Atlantic. But only a minority of model simulations present these extreme scenarios. Most model simulations predict the system will end up in the Gulf — while subtle nuances in atmospheric steering currents will determine where the storm ultimately makes landfall. A small piece of good news is that if the storm makes landfall in the northern or western Gulf of Mexico, dry air from the north may weaken it slightly. However, that’s not much comfort when almost the entire Gulf region is warmer than average during the most active time of the year for hurricanes. If the storm tracks further east, it could avoid dry air. That would be a concern if any potential track brings it closer to Florida.
