Discussion of Intense Tropical Cyclones

[Ptarmigan]

While looking back at some satellite imagery from Maria '17, I noticed an interesting feature around the time of peak intensity. Just before 00Z September 20th, there was a large and cold convective burst near the edge of the CDO (still image below, loop here). I'm not sure this phenomenon has a proper name, so for now, I'm going to call it lobing.

https://www.nrlmry.navy.mil/tcdat/tc2017/AL/AL152017/png/Infrared/201709192330_AL152017_abi_Infrared_80.0_covg100p0_res1km.png

Based on recon data, it appears like it might have coincided with a halt in intensification since the previously falling pressure evened out at 909 mb at the 2219Z pass and only varied by a millibar up and down from that number for the next six hours before rising. This lobing phenomenon could possibly be associated with structural changes. Lobing isn't exclusive to Maria '17 either. It appears it has occurred with a number of intense tropical cyclones across multiple basins. Some of the more clear examples are Nepartak '16, Patricia '15, Usagi '13, and Gilbert '88. Patricia '15 and Gilbert '88 each had recon near the time of lobing (near 18Z October 23rd for Patricia and 00Z September 14th for Gilbert), and both cases were similar to the Maria '17 data which showed no appreciable deepening from that time on. Patricia '15 actually began to weaken rapidly, although land interaction may have played a part in that case. Regardless, it may be a good sign to indicate whether an intense tropical cyclone has peaked.

I have noticed thunderstorms near the central dense overcast (CDO) and surprised there is no term for it. I tend to notice those thunderstorms east of CDO when they are past their peak. I have seen that with Katrina before it made landfall.

[kevin]

In the last 10 years there have been 13! category 5 hurricanes in the Atlantic. No other time period in the satellite era has had a comparable number of such intense hurricanes in a 10-year time span. How much individual events are correlated to a long-term climate situation is of course difficult to quantify, but imo a pattern is starting to become visible. Since the Atlantic has had excellent recon since the start of the satellite era the argument that previous intense storms were missed doesn't hold here. Is it possible that, as some research has proposed, the higher SSTs due to climate change don't per se result in a large increase in TCs or MHs, but do cause the 'big ones' (aka high-end cat 4/5s) to get even bigger than before?

The MDR is still the 3rd warmest it's been on record (behind 2024 and 2025) and the Gulf is by far the warmest it's ever been on record this time of the year (probably since no big storms formed there so far this year, akin to the WCar before Melissa). Since shear in the Gulf this late in the year is highly unfavorable I don't expect anything to form there anymore, but otherwise it has just as much untapped potential as the WCar had before Melissa. As we saw with Melissa or f.e. Erin en Beryl recently there has to be just a tiny region and time period with favorable conditions and then the scorching SSTs can result in RI & often a cat 4/5. Unfortunately, these sort of climate debates often unnecessarily devolve into political debates, which is unfortunate since it is one of the most interesting and important discussions to have in this field of study. Since there is overwhelming scientific consensus that the current warming of the planet and the ocean will continue at an unprecedented rate for the forseeable future, I guess we'll just have to wait and see whether the high number of cat 5s recently has been a statistical anomaly or a pattern due to a changing background state.

Note: of course we're looking at just one basin here. In the Australian region the number of category 5 severe tropical cyclones is ~25% above the long-term average in the last 10 years. In the South Pacific the number of category 5 severe tropical cyclones is ~50% above the long-term average in the last 10 years. The WPac is the only basin where the number of super typhoons is similar in the last 10 years as the long-term average, even about 10% below the long-term average. However, due to a more inconsistent archive in the WPac with a long period without recon the numbers in the Atlantic are more trustworthy imo.