John catches Mexico off guard; PTC Nine threat to Cuba/Mexico/Florida

The big picture is John (EP10) very rapidly intensified into a Category Three storm and turned towards the northwest, and is now pounding Acapulco, which is still recovering from last year’s Hurricane Otis. On the Caribbean/Gulf of Mexico side, Potential Tropical Cyclone Nine (AL09) is still rather disorganized, but all the signs are it will develop into a major hurricane once it enters the Gulf of Mexico tomorrow.

The official word on these two storms may be found in the key messages products from NHC:
Key Messages regarding Potential Tropical Cyclone Nine (en Español: Mensajes Claves)
Key Messages regarding Tropical Storm John (en Español: Mensajes Claves)

John made landfall overnight, surprising everyone by rapidly intensifying from a borderline hurricane to a Category Three storm in less than 24 hours. It also made an unexpectedly sharp turn to the northwest, and is now located near the resort of Acapulco. You may recall that Acapulco was severely damaged by Hurricane Otis last year, damage from which the area as (controversially) not yet recovered.

Right now the big threat from John is rain. The storm is expected to loop offshore and could potentially pump over a meter of rain (over 3ft) into the coast, including Acapulco. Mudslides and flash flooding are a certainty, as is a lot of misery for an area that has seen a lot of that in the last year.

On the other side of Mexico, Potential Tropical Cyclone Nine is brewing up. While still disorganized, it is showing some signs of spinning up this morning as it moves towards the Yucatan straits …

Here is the latest impact forecast, running the official NHC track and intensity estimates through my TAOS(tm) TC model:

On this track it will make landfall in the relatively sparsely populated Big Bend area of Florida, causing somewhere between $6 and $8 Billion in damage there and in southern Georgia. But a wobble or larger wind field will cause more damage to the target-rich environment around Tampa, which could easily double the damage or more. This time of storm paralleling the coast is extremely hard to forecast for that reason: the wobbles matter, a lot.

In the forecast landfall area, expect at least a Category Two storm, and upwards of a Cat Four isn’t out of the question. Along the Florida coast hurricane conditions are a given. If this track holds up, from Cedar Key to Tallahassee/Port Leon will get hit hard, with the region from Panama City to Gainsville within the high wind swath. The Tampa/St. Pete/Clearwater area are at risk of a side swipe depending on storm size and intensity and need to prepare just in case – a few miles will make all the difference, and we simply can’t forecast that. South Georgia is also going to get hit hard, with high winds, rain, and probably a tornado or three, with the core damage swath passing right over Valdosta and Tifton. Wobbles will matter, but the entire region inland from Albany to Eastman to Waycross should be ready for hurricane conditions.

The big fear about PTC9 at the moment is for rapid intensification. All the ingredients seem to be there, and while the fast forward speed that should develop once it enters the Gulf would normally cap development, the models are quite enthusiastic. This plot shows the intensification forecast for some of the major models:

As you can see there is a very prominent spike before landfall in about three days (72 hours). The big difference between the official forecast (black line) and the more enthusiastic models (greenish spikes) is forward speed. Even a few hours longer over the warm fetid waters of the Gulf means the potential for the storm to gain strength. This is why I keep saying that until the storm actually enters the Gulf and begins the northward turn, we won’t really know now fast it is going to move and therefore how strong it can get. Another factor is how far offshore the Florida Peninsula it stays – the closer to Disneyworld, the more strength will potentially be sucked out of the storm (ok, it’s the land, but the analogy works). But virtually all of the models have the future Helene looping far enough offshore so that the mouse won’t be able to steal her wallet (figuratively speaking of course). Here are the GFS and ECMWF forecast model runs, both the primary and ensemble runs (in color) and individual ensemble members (which, as you recall, aren’t to be taken individually as independent forecasts, but as indications of the uncertainty in the main forecast):

So this is a remarkably consistent forecast for a storm that, strictly speaking, doesn’t even exist yet except as a disorganized mass of thunderstorms.

So what about coastal Georgia and South Carolina, including the Frogmore metroplex (Savannah/Beaufort/HHI), not to mention more envious cousins to the north, west, and south? This is the classic inland version of the back door storm, in some ways reminiscent of last year’s Hurricane Idalia, although PTC9 (future Helene) should stay more inland and curve west rather than go back offshore. Right now it looks like gusty winds right at tropical storm force on the coast and a bit less inland, rain but certainly no where near “Debby” levels. There is a concern that the winds will start to blow onshore and the high tide Friday morning might cause some shallow coastal flooding in the usual places. Right now it looks like that may be at about 10ft MLLW at the Fort Pulaski gauge, which means:

9.5 – At 9.5 ft MLLW, minor coastal flooding occurs. Flooding will begin to impact Shipyard Road to Burnside Island. Parts of Ft Pulaski National Monument will begin to flood, including several trails. Flooding will also begin to impact Tybee Island including Catalina Dr and Lewis Ave. In Bryan County, water could breach docks near Ft McAllister and flooding will impact portions of Mill Hill Rd. In Liberty County, flooding impacts the Halfmoon Landing area and Cattle Hammock Rd near Bermuda Bluff subdivision.

At 10.0 ft MLLW, moderate coastal flooding occurs. Shipyard Rd will be impassable, isolating residents on Burnside Island. Water will start to encroach on HW-80 and as the tide gets closer to 10.5 ft MLLW, could begin to cover portions of the roadway. Flooding will expand on Tybee Island and Catalina Dr and Lewis Ave will be impassable. Flooding will also impact Wilmington Island, the Coffee Bluff community, Ossabaw Island, Sapelo Island, and portions of HW-17 south of Darien.

Timing is that conditions should deteriorate during the day Thursday in Savannah, with the worst right at Midnight with winds right at tropical storm force, and remain bad until around noon Friday. For the Frogmore/Beaufort area, those conditions will occur about an hour later for Savannah. Farther south, around Brunswick, conditions will start earlier (Wednesday evening), be worse (peak winds in the 50mph range), and last longer, clearing out Thursday morning. Inland the timing will reflect the coast, but may in fact be a bit worse depending on the exact track and how organized the storm stays after landfall. Across the region there will be gusty winds and that means power outages, limbs down, probably some trees especially more inland (Statesboro, Dublin) and south (Waycross). Tornadoes and water spouts are always a risk, so you know Nicholas will be sitting on his weather radio during the storm.

That’s what it looks like right now. Unfortunately, as noted yesterday, we won’t have much confidence in this forecast (at least I won’t) until the storm actually spins up and enters the Gulf. If you are in the watch and warning areas, pay attention to local emergency management and get ready. If in GA/SC, replenish your snack supplies, there will likely be coastal watches and warnings. I never like to second guess local authorities but expect early closures Thursday and late openings or all day closures Friday.

Next big update from me tomorrow morning, when the storm should be in the Yucatan straits, but will post a note if/when the storm becomes tropical.

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