BMS Tropical Update 9/4/2018 1 PM CDT
The Parade Begins
On Friday, I mentioned that the peak of the hurricane season could live up to its climatological peak. Over the Labor Day weekend, Tropical Storm Gordon formed over the Florida Keys and is currently 130 miles SSE of Mobile, AL. Potential tropical cyclone 6 that was off the Africa coastline on Friday which has now become Hurricane Florence and is tracking across the Atlantic and is currently 1270 miles ENE of the Lesser Antilles. As of this morning, another tropical system which may eventually become Helene over the next 5 days is currently tracking a few hundred miles SSE off the Cabo Verde Islands. and has a 70% chance of development over the next 5 days. To add to the parade, the long range forecast models are predicting another strong African wave later this week which has the potential to become Isaac in the longer term.
All eyes should be on Gordon at this time, and to a lesser degree, on Florence as well. Gordon will have the most immediate impact on the insurance industry, but the good news is that time is running out for Gordon to become more organized over the warm waters of the Gulf of Mexico. Gordon should make landfall near Gulfport, MS later tonight as a strong tropical storm or weak hurricane. As of this morning, Gordon appears to be disorganized as it is being squeezed between two upper level lows, which is not an ideal pattern for strengthening. Typically, named tropical cyclones like an environment of a large ridge or anticyclone aloft for optimal strengthening, which is not the case currently. Gordon’s most severe impacts are heavily skewed to the right side of the storm where most of the organized convection exists.
The biggest impact Gordon will have is rainfall along the central Gulf Coast states. As much as 4 -8 inches of rain is expected to fall along Gordon’s track up into the lower Mississippi River Valley. Due to Gordon’s small size, storm surge flooding should be manageable for many of the coastal communities with 3-5 feet of surge currently being forecasted by the NHC across some of the coastal islands. Gordon is expected to continue strengthening right up until landfall, with the strongest winds being on the right side of the track up into Mississippi. The weaker winds will likely occur over much of Louisiana as Gordon moves inland.
Although Gordon is making landfall at a different angle than Hurricane Nate last year the lopsidedness of Gordon is currently very similar to Hurricane Earl that made landfall in 1998 which did not trigger a PCS Catastrophe Bulletin when it made landfall as a Category 1 hurricane. However, we have seen hurricanes like Isaac 2012 result in large insured loss up to $900M because the strongest winds track across New Orleans, which is not forecasted to occur with Gordon at this time.
Over the long weekend, there were some pretty exciting forecast scenarios for Florence impacting the East Coast of the U.S. Most of those scenarios have been removed at this time, however, with the higher likelihood of Florence recurving before it threatens the East Coast of the U.S, but (there is always a “but” in the forecast) Florence is currently fighting a large area of dry dusty air known as the (Saharan Air Layer) SAL. As mentioned in Friday’s blog post, if Florence stays weaker it will have a better chance at moving in a westerly direction. Over the weekend, the ensemble guidance had a cone of uncertainty that stretched the width of the Atlantic Ocean. It is expected that Florence will fluctuate over the next several days, but by the end of the week it could be in a better environment. This will allow Florence to strengthen into a stronger hurricane as it approaches the east side of Bermuda over the next 5 days, where there is a favorable overall environment for storms to become stronger. Bermuda still has the highest chance of impact from Florence, but a track west of Bermuda can’t be ruled out yet. There is some forecast uncertainty, with energy from recurving Typhoon Jebi (which made landfall in Japan last night) likely influencing the Northern Hemisphere Jet stream over the next 6-10 days.
Other Storms in the Parade
Over the next week or so there will be a parade of tropical waves that will emerge off the coast of Africa. Every one of these systems will have the potential to develop into a named storm, and the long range forecast suggests that the tracks of these future storms will have a better chance of making it west. The good news is that it appears the Madden–Julian Oscillation (MJO) will be in a suppressive stage near the end of September and could subdue any new tropical development over the Main Development Region.Below is just one deterministic model run from the ECMWF but there appears to be five tropical systems over the next 10-day forecast period. Florence re-curves, but there are two more storms at lower latitudes that bear watching in the longer range. Source: WeatherModels.com and Ryan Maue