Do you remember the last time a hurricane started in Missouri?
To be clear, there is no hurricane yet, and no certainty that one will develop, but it is possible, and it won’t be developing over Missouri, but the trough of low-pressure that may help trigger a tropical system was there just a few days ago.
The National Hurricane Center is monitoring the northeast Gulf of Mexico for the likely development of a tropical cyclone later this week, possibly as early as late Wednesday.
This system will be the result of a low-pressure trough dipping southward across the central United States into the Gulf of Mexico, where warm waters combined with high pressure aloft may allow a surface circulation to form that will become a tropical depression. It will be named Barry if it reaches tropical storm status, with 39 mph sustained winds around a closed, warm-core circulation.
At the time the forecast models started catching on to this system over land moving southward and possibly seeding a tropical system in the Gulf, it was over Missouri. When the National Hurricane Center first circled the northeast part of the Gulf for possible development, the low was centered over Memphis.
It’s a bit unusual to see a Gulf of Mexico tropical system form from such a southward-dipping trough over the central U.S. However, it is not at all unusual for something moving off the U.S. coast from inland — a storm cluster or stalling front or disturbance of some sort — to help trigger a tropical cyclone.
In the bigger picture, many hurricanes develop from weather systems that have crossed a land mass before moving over the ocean. Many of our bigger Atlantic basin hurricanes in August through October originate from storm systems moving off the coast of Africa into the Atlantic ocean.
A low-pressure over land and a tropical cyclone over the ocean are not structured or fueled the same.
A typical low-pressure system, or baroclinic cyclone, forms along the boundary of differing air masses with stronger winds aloft. Conversely, tropical cyclones feed off the energy of evaporating ocean water at the surface, and develop best when winds are weak aloft under high pressure, preventing the tops of the developing tropical convection from being sheared away and allowing air to be evacuated rapidly from the upward spiraling circulation.
This difference in formation and evolution means it is never automatic that a storm system moving from land over a warm ocean will become a tropical system, or, in a topic for another day, that a tropical system making landfall will covert into a significant storm system over land.
But when conditions are just right, it is possible for the low-pressure system moving off land to develop convection over warm ocean water, which then attains a circulation rooted near the surface and becomes a tropical cyclone.
Beyond some uncertainty about whether this tropical cyclone will actually develop, there remains great uncertainty about how intense it may become and what its eventual track would be.
It appears likely that high pressure over the Rockies will tend to pull the system more westward, toward Louisiana and Texas, rather than allowing it to simply head east or northeast for a landfall on Florida.
This could change if a strong trough of low-pressure near the Great Lakes and its associated cold front, which will give us our next widespread chance of storms on Thursday, is strong enough and/or south enough to nudge it more north or east.
For our region, it appears unlikely we will see major impacts from the early stages of a tropical system. Even if it were to make landfall along the rents would only allow a slow drift north as opposed to the faster movement we would typically see with a similarly placed tropical system in autumn, like last October’s Michael.
A more likely scenario at this point is that the possible tropical storm or hurricane drifts west, comes ashore somewhere between Galveston, Texas, and Biloxi, Mississippi, then some of its moisture gets circulated north and east in a scattered fashion next week.
Some of that could possibly affect us next week, but not do anything more than augment scattered afternoon pop-up storms resulting from daytime heating.
Ironically, the tropical system’s remnant low may end up moving right back toward Memphis and Missouri where it came from.
Weather Journal appears on Wednesdays.