It is an ugly, small, and not very angry storm. But that doesn’t mean it won’t cause problems. Just ask Florida.
Tropical Storm Eta is in the Gulf trying to reorganize itself in the face of dry air and some shear. It has a difficult life ahead of it (humans aren’t complaining) but there is still a chance it can cause another round of significant impacts for the United States before it dies.
From the NHC
Eta’s convective pattern now consists of mainly a compact ring of inner-core convection with cloud tops of -60C to -70C. The earlier main outer convective band located in the northeast quadrant has weakened considerably, and the inflow into that feature is now being shunted westward into Eta’s inner-core region.
Visible and water vapor satellite images also indicate that weak anticyclonic cirrus outflow has recently developed over the inner core. The last recon pass through Eta a few hours ago showed a pressure rise to 997 mb that was followed by a pressure decrease to 995 mb on the last pass. Both flight-level and SFMR-derived surface winds had also decreased and only supported around 45 kt, which is the initial intensity used for this advisory.
The initial motion estimate is southwestward, or 235/14 kt. Mid- and upper-level water vapor images show a cut-off low located over the extreme northwestern Caribbean Sea near the Isle of Youth. This feature, in conjunction with a deep-layer ridge extending across Florida and the Gulf of Mexico, is expected to produce northeasterly flow that will keep Eta moving southwestward for the next 24-36 hours.
However, the cyclone will gradually slow down during that time as a broad deep-layer trough moving across the central and south-central U.S. weakens the ridge over the Gulf, causing Eta to stall or make a small loop around 36 hours. By 48-60 hours and beyond, the aforementioned trough is forecast to lift out to the northeast, allowing at least some of the Gulf ridge to build back in, slowing down Eta’s poleward progress or even possibly trapping the cyclone over the northeastern Gulf of Mexico.
The global and regional models are in very good agreement on the developing track scenario through about 72 hours, and then diverge significantly thereafter, with the bulk of the guidance taking a much weaker Eta northwestward or northward into strong shear conditions.
However, the Navy COAMPS-TC model strengthens Eta to near major hurricane status and takes the cyclone northeastward, while the HMON model also intensifies the cyclone into a major hurricane, but leaves it trapped over the southeastern Gulf of Mexico. The latter two scenarios are considered to be outliers due to the abundance of very dry air surrounding Eta and an expected increase in the deep-layer shear to more than 25 kt by 96 and 120 hours. The new official forecast track is to the left or west of the previous advisory track, but not as far west as the consensus models, which take a significantly weaker and more shallow cyclone toward the north-central Gulf coast.
Some re-strengthening appears more likely now that Eta has shed a lot of outer convective baggage and has become more compact, and has developed a donut ring of inner-core convection and some modest upper-level outflow in all quadrants. Eta’s best opportunity for intensification should come during the next 36 hours when the cyclone will be moving over the warm waters of the Gulf of Mexico Loop Current and the deep-layer vertical wind shear gradually decreases to less than 10 kt.
Although occasional intrusions of very dry air will prevent rapid intensification from occurring, some gradual strengthening seems to be in order given the other favorable environmental conditions and the cyclone’s new smaller size. By 48 hours and beyond, increasing vertical wind shear and dry air entrainment should cause steady weakening of the cyclone through end of the forecast period.
However, if Eta takes a more northwestward track like some of the NHC model guidance is indicating, then the cyclone will get sheared more and weaken sooner than indicated in the official forecast. The new NHC intensity forecast is similar to the previous advisory, and but is lower than intensity consensus models IVCN and HCCA, which re-strengthen Eta to a 65-70 kt hurricane.
Model Data
The tough thing with this storm is there are many moving pieces all showing up at different times. While normally during the summer, the number of “puzzle pieces” for these systems is like two or three, in total, for Eta it is two or three during the next 48 hours, then a different two or three between 48 and 120 hours. Then another two or three after that.
So the model guidance isn’t – likely – as reliable as normal with this system. And – likely – any system that forms in the Caribbean or Gulf through the remainder of the season.
And this isn’t necessarily unusual. It is just how things go this late in the season. Typically, though, we don’t have system forming south and entering the Gulf this late in the year.
Right now, though, the guidance is a big ‘all over the map’ with track guidance.
For now, I’m going to hold on to the Euro and GFS for a better idea of forecast track due to the physics the model uses to formulate forecast data. It isn’t that these models are “better” in general, they just may be “better” right now.
Both show Eta drifting north and then getting pushed west, then moving north again and making landfall along either the Louisiana / Mississippi / Alabama / Florida coastline l;ate this week and into the weekend and/or early next week.
That is a wide-open alley north, but, at this point, the model data supports a lot of potential outcomes.
Intensity guidance is – in my opinion – almost useless.
While there is consensus between the model data, I think the models are struggling too much right now to offer an accurate look at intensity. Furthermore, due to the drastic differences in track, and the track is likely set to dictate the intensity, I have a difficult time trusting any data.
Bottom Line
I can not know – specifically – where Eta will make landfall a second time. In fact, there is still a chance it gets eaten up by one of the two cold fronts / troughs anticipated to interact with the system during the next five days.
Right now, it is important to keep tabs on this system for future impacts by this weekend for sections of the northern Gulf Coast.
Those impacts are most likely going to be heavy rain, potential flooding, gusty wind and the potential for tornadoes. It is unlikely – though, not impossible – for this to become a Major Hurricane and produce Major Hurricane-like conditions or damage along the northern Gulf Coast.
Just please keep tabs on the forecast and keep up with the latest on Eta so you can be prepared for what is to come.
Today’s Severe Risk
Today’s Tornado Risk
