Windspeed

The past few days have been glorious.

I'm inclined to believe what we were seeing on radar in terms of a moat was just a massive feeder band rather than an outer eyewall

Love getting these Guam reflectivity shots on this monster...

Again, they are so very lucky. Champi continues to intensify. Also, note the very intense meso in the northern eyewall at the end of this animation with the bright purple reflectivity. Amazing...

No doubt Champi is very intense at the moment. In the above radar, you can see the intense mesos rotating within the eye. The IR tells the rest below. Guam is so incredibly lucky this isn't barrelling due west at just a few ticks higher latitude.

Guam may come out of this very lucky. It looks as if the northern eyewall may only just graze or even miss the southern shoreline. The inner core winds will remain entirely offshore.

Amazing eyewall around 'Champi' via NWS Guam radar.

The Mexican shoreline is getting raked by Simon. However, Simon's small core is a frog's hair distance offshore to avoid weakening versus strengthening any further. It's a delicate balance that's preventing Category 5 intensity but not yet detrimental enough to induce weakening. Still, the abrupt change in elevation near the coast and such influence on inflow will still disrupt Simon and should begin to weaken it if the core parallels the coast any closer. Granted, that means very little with respect to flash flooding that is underway with moist low-level southerly fetch within the eastern circulation feeder bands and orgographic lift.

It seems like we always have to beat it into people's skulls during landfalls. It's the maximum sustained winds possible as an estimate over water for a reason. It's a marine storm before it is a land storm, and advisories have to account for what is occurring in real time over the ocean surface for any poor ships/souls that might find themselves in the worst scenario. But due to frictional convergence / drag, you will almost never see those sustained winds over land unless you have a super intense eyewall with embedded multiple mesos rotating around that overcome frictional forces with insane ground level velocities. As a general rule, the highest wind reports over land are always in gusts due to this process. You might get those highest sustained winds right on the immediate beach/shoreline perpendicular to the onshore motion of the inner edge of the eyewall, but the equipment would need to be in the right place at the right time and that is exceedingly difficult placement and timing to pull off. Interestingly, and as no surprise, the instrument anemometers that have been positioned in the right place and at the right time during past landfalls that recorded sustained winds near maximum have generally failed during that event.

I also need to add that the reason most immediate advisory packages don't rapidly ramp down maximum sustained winds after landfall is twofold: 1) part of the eyewall or outer eyewall may still be over water, 2) any large estuaries even after landfall may still experience maximum winds. Once the entire circulation is inland, subsequent advisory packages tend to ramp down quickly.

Simon appears to be doing what most EPAC hurricanes have done this year. It's undergoing rapid intensification. A pinhole eye has formed in the direct center of the tiny CDO. This is a microcane for now and on it's way to becoming a major hurricane today. It will most likely grow in size over the weekend. It's tiny core will expand, and the pinehole eye should give way to a larger eye eventually.

Isaias has intensified overnight. NOAA and Air Force Reserve Hurricane Hunter data showed that the maximum flight-level winds have increased up to 107 kt, with a better-defined eye and a shrinking eyewall. These changes are also present on satellite imagery, with a more symmetric presentation along with a warming eye/cooling eyewall. The available data suggest a current intensity of 95 kt for this advisory.

Isaias will likely become a major hurricane soon with the improving satellite imagery, and it could continue to intensify for the next 12 hours or so while it moves over very warm and deep water. However, a large increase in shear is anticipated before landfall, which will probably cause some weakening to occur. This is a tenuous spot because it would only take about a 6h delay in the onset of the shear to bring a stronger hurricane than expected onshore. The new forecast explicitly is a bit higher than the last one, but our best forecast at this time is for a high-end category 2 intensity at landfall, which is about the same as before. Regardless of its exact wind speed at landfall, Isaias will be a dangerous hurricane with significant storm surge, damaging winds, and flooding rains. The wind field is also predicted to grow due to a trough interaction, and some of these impacts will extend well away from the center. After landfall, gusty winds are expected to reach well inland over portions of the southeastern United States.

Isaias has turned towards the north-northeast (020/13 kt), and the hurricane is expected to turn northward and accelerate later today due to increasing flow between an upper trough near the northwestern Gulf Coast and a subtropical ridge extending across the western Atlantic. Landfall is expected to occur within the hurricane warning area Friday night or early Saturday. The new forecast is almost the same as before, very near the Google DeepMind guidance, which has been very accurate for Isaias.

Key Messages:

1. A life-threatening storm surge is expected from the Mouth of the Mississippi River to Suwannee, Florida. Residents in the warning area should follow advice given by local officials and evacuate immediately if told to do so.

2. Damaging hurricane force-winds are expected over portions of the Florida Panhandle, southern Alabama, and southern Mississippi where a Hurricane Warning is in effect. Residents in these areas should prepare for the possibility of long-duration power outages.

3. Damaging wind gusts are possible over much of central and northern Alabama, extreme eastern Mississippi, and portions of western and northern Georgia, especially in areas of higher terrain. Additional Tropical Storm and High Wind Watches and Warnings may be required for portions of that area later today. Residents should secure loose outdoor items, avoid driving high-profile vehicles, and prepare for power outages.

4. Isaias will bring areas of heavy rainfall to the central U.S. Gulf coast and much of the Southeast through the weekend. Considerable flash and urban flooding, along with significant river flooding, will be possible.

FORECAST POSITIONS AND MAX WINDS:

INIT 09/0900Z 26.4N 88.0W 95 KT 110 MPH 12H 09/1800Z 28.4N 87.3W 105 KT 120 MPH 24H 10/0600Z 31.0N 87.1W 65 KT 75 MPH INLAND 36H 10/1800Z 33.5N 87.5W 35 KT 40 MPH POST-TROP/INLAND 48H 11/0600Z 35.5N 86.7W 25 KT 30 MPH POST-TROP/INLAND 60H 11/1800Z 38.2N 83.1W 15 KT 15 MPH POST-TROP/INLAND 72H 12/0600Z DISSIPATED

4:00 AM CDT Fri Oct 09
Location: 26.4°N 88.0°W
Moving: NNE at 15 mph
Min pressure: 963 mb
Max sustained: 110 mph

Satellite continues to improve, and we have a warming clear eye now. Category 3 is looking much more likely. If they don't pull the trigger in the 4AM CDT package, they probably will later with an intermediate advisory.

Best structure Isaias has had in its lifecycle so far. Perhaps a window here for some brief intensification prior to increasing shear today.

Strikes me as one of those N GOM collapse-deals, like Opal or Ivan....

Looks like we're going to have quite a battle of timing and walking thin ice with that shear axis. Might be a back and forth between 6 hr runs on the TC model suites today until they get a better feel for track motion, and if/when the mid-level shear begins encroaching. For example, the 18z HAFS suites kept intensity in check, preventing a major. The 00z suites kept the core on the edge and bombed Isaias into a strong major. The recent 06z runs are back to allowing encroachment in the mid-levels again, though it may still be reaching Category 3 / 960s prior to weakening. We'll have to see if the 12z suite swing back to flirting with the 940s and a more significant major.

Best track is now 35 kts and upgraded to TS Isaias for the next advisory package.

00z HAFS suites are significantly stronger versus 18z. Intensification is faster, with a major hurricane down into the 940s passing east of the mouth of the Mississippi River. Both still show disruption from increasing shear by landfall, but obviously, this would be troubling for surge impacts along the Mississippi, Alabama, and western Panhandle coastline.

Intense bursting of convection now over the NHC's 10PM CDT advisory position:

Anyone have latest links for Tomer Burg super ensemble and TCHP maps? Been away during the CONUS tropical respite over the past couple of years and some of my links seem to no longer be valid....Tomer seems like he is moving his stuff around.
Found this one for TCHP, but don't love it.
https://cwcgom.aoml.noaa.gov/cgom/OceanViewer/index_phod.html#
This was my go-to, hasn't been updated for a couple of years.

https://www.aoml.noaa.gov/phod/goos/gliders/images/tchp_conditions_latest.png

The first runs of the HAFS suites since classification are not impressive, to say the least. The TC gets walloped around 70'ish hours out and becomes very assymetric with advected dry air doing its thing. Something to keep in mind. Is the window there for a strong hurricane? Sure. But the TC needs to come together rapidly over the next 48 hours.

I think this gets up to a major before it gets closer to the coast. The gulf has so much heat in it... just jet fuel for it. And if it slows down at all? 

It’s supposed to pass right over the loop current. And the tail end of a trough is often quite favorable. There’s a lot of moving pieces but a hurricane landfall looks plausible at the moment.

This system has escalated quite a bit from what the original thinking was. Definitely some potential for a strong hurricane especially in the middle of the gulf 

00z GFS was much more realistic with the progression of this system and the synoptic setup. Though it does still bring the TC to hurricane status in the southern and central GOM, significant weakening occurs by landfall due to all the aforementioned issues discussed previously.