Windspeed

Much has been discussed in various tropical cyclone threads on this forum and the old predecessor Eastern Wx forums over the past 17 years about the northern Gulf of Mexico and its unfavorability in sustaining major hurricane landfalls. Even as recently a Hurricane Nate, the discussion was brought up again. Though Nate was not a major hurricane, nor was it forecast to be, it was forecast by the NHC to reach 90 kts / 105 mph by landfall. Nate did not reach Category 2 intensity however, and even appeared to weaken more significantly than the official advisory prior to landfall; though we will need reanalysis to perhaps know for certain just how much weakening occurred. Either way, it is clear Nate did not strengthen or maintain its structure into landfall. Convection waned, the core appeared to collapse and the NE eyewall barely held its curved banding into the MS coastline. As such, discussion linked Nate to the unfavorability that exists there. I disagree with this conception, however. Hurricane Nate is not a good example of a cyclone sustaining intensity due to SST environmental conditions. Nate was a hurricane with a small core that was under a extremely fast steering regime. Convective mesos would form, rotate to the western half of the circulation and collapse. This happened at a near constant rate as its forward motion increased until it couldn't manage to close off its eyewall vortex. At multiple points on track, an eyewall would develop only to pivot around into a new intensifying meso. I think recon may have measured hurricane force winds within the stronger east side of these mesos, but I am not so sure Nate ever held a steady state intensity for prolonged periods. It's quite possible the core would reattain hurricane force during each meso, but an eyewall band had trouble establishing overall dominance as the core vortex feature. Whether the shallower heat content had an effect I believe is insignificant compared to the unfavorable flow against the western half of the hurricane. Perhaps radial convergence and evaporation feed of heat flux really was suffered by Nate. The storm was just moving way too fast for it to take advantage of any immediate sea surface heat layer, much less heat content at depth (regardless of its presence). Understand that I have been skeptical of forward motion, low-level convergence and heat flux being a significant factor, but I am now wondering if this is a critical to sustainment of eyewall convective banding as upper-level divergence over LLC core may be overwhelmed or disrupted with meso scale vortices updrafts within the inner periphery of the low-level vortex in rapidly moving systems such as Nate. This may not have been as much a negative factor for an already well-organized surface vortex, but Nate seemed to be struggling with this process even as a hurricane. We also have plenty of examples of hurricanes intensifying at landfall in the northern Gulf over the shallow surface layer to contend with the hurricanes that weakened. Alicia, Fredrick and Camille (after completing an ERC) are some of the more notable cyclones. The most intense major hurricane to be shown to have reintensified by landfall in reanalysis is Camille. Though it weakened during an ERC SSE of the mouth of the Mississippi River when the tiny inner eyewall finally collapsed, a bright outter ring representing the outter eyewall contracted quite rapidly. It did not lose its structure and in fact appears to have sustained nearly a 360° 12 nm closed band right at landfall at Waveland, MS. See linked animation .gif of landfall and PDF of reanalysis. Now clearly, shallow surface layer SSTs in August near the northern Gulf coastline are warmer than in October. We typically observe 29-31° C shallow surface water by late August without any significant frontal interaction. By October, the shelf typically drops a few degrees. But 28° were still being observed in Nate's track. That would have been sufficient to support a major hurricane, especially a fast mover. Unfortunately, Nate was moving so fast, it began to collapse before the shallow layer even mattered. We have seen rapid motion in major hurricanes before. Charley was moving around 20 mph when it underwent rapid intensification from 95 to 125 kts and a 27 mb pressure drop in less than 8 hours. But when Charley's core gained faster forward motion, it already had a well organized and symmetrical core. Interestingly, though it did not cross over the northern Gulf shallow shelf, it was crossing the shallow shelf off of SW Florida, north of the Keys. Wilma also intensified crossing this shallow shelf. OTOH, Nate was in the process of developing its core vortex the entirety of its track across the W. Caribbean and GOM between 22 and 26 mph. These are purely tropical cyclone examples. We can also cite the rapid motion of the 1938 Long Island Hurricane; however, this storm was likely undergoing rapid baroclinic forcing as well, which likely sustained intense convection and major hurricane force winds/surge straight inland. Some majors that weakened at landfall are obviously noteworthy. Katrina, Rita and Ivan are mentioned frequently. But every one of these systems were battling significant shear as well. Ivan is an interesting case as it managed to remain 105 kts Category 3 even with 30 kts of mid-level shear advecting dry stable air into its core. The northern and eastern eyewall band held together quite well. With past hurricane examples of intensifying storms into the northern Gulf coast, these systems were all in a more favorable upper-level environment. Even though Nate was in a low shear environment, the western circulation northerly flow was hampered by such strong opposing directional mid-level flow. I think if Nate had been a slower moving storm, being a purely tropical entity, it would have been able to reach Category 2 intensity at landfall. Perhaps even strengthen all the way into landfall. But this is speculative. I'm only wanting to point out that the sea surface environmental aspects were not its doom. Edit: I initially intended to preview and correct typos, but I accidentally submitted the entire post prematurely. If you read this post within the first hour of submission, you may want to reread before commenting. Thanks!

Often times posters will discuss, compare and contrast historical tropical cyclones and their climatology during an active event thread, but these posts end up buried amongst the overall meteorological storm discussion for obvious reasons. I am opening this thread for current and future discussion as it relates to past tropical cyclone events and their peer-reviewed reanalysis projects. If any person wishes to post about, reminisce or debate past tropical cyclones, regardless of oceanic basin or sea, perhaps they carry that on in this thread so we may have an easier flow of information and archive of such discussion. I have quite a few cyclones to discuss myself and existing preconceptions / misconceptions about a particular region of the Atlantic to flesh out. My first post will be later this evening. But don't wait on me.

I was actually using the NOAA/NCEP's GOES SST data from the 23rd before Maria's cloud canopy obscured it. This is where satellite derived products come from. In any event, 25° isotherm cold pool upwelling just wasn't showing up. There were 27° showing in Jose's wake in this image close to last 24 hour position of Maria's core when plotting, but definitely not the 24-25° SSTs that recon found. Hence, Don's point. Can't beat recon and bouy data (when available).

Maria is currently over 27.5-28°C SSTs. I think the bigger issue is the large size of Maria's circulation, expanded pressure gradient and dry mid-levels. Being a large system, pulling airmass off of the SE CONUS is most likely having some effect. Still, the upper environment is excellent and the core could just as easily convect up again. Edit: RE: SSTs You just can't beat recon data. Satellite data is off place or lagging in showing Jose's colder pool upwelling from depth a little further east with respect to Maria's core. But again, recon is recon. That being the case, Maria would need to gain longitude and get closer to the Gulf Stream. Not likely for a while, given track. Therefore, further weakening seems the order of the day.

Thereabouts. Must have been pretty extreme.

Haha, JB? Never... This close, I wouldn't outweigh model consensus. Land interaction of the eyewall still remains an outlier. But obviously the prospect of a partial grazing, especially of outer banding, remains a real possibility for the Outer Banks. Maria has a large circulation and strong convective bands may mix down NE winds of hurricane or at least strong TS force.

I care, Steve, I care... [emoji45] Recon data suggests a large area of hurricane force winds to the north of the center. Maria has grown significantly in size over the past few days. The gradient has expanded. Though it is no longer a major hurricane, the windfield may present some problems for the Outer Banks. Maria is not the sloppy sheared system that Jose was as it moved north. Maria is still in a favorable environment and should maintain strong convection on closest approach. Bands with upper TS and Category 1 force NE winds are quite possible at OBX/Hatteras.

Maria is getting her act together this evening. A nice ring of -80° C cloudtops encircles the eye. There is still some high cloud debris in the eye, but she looks to be intensifying. Next recon should be interesting.

The GFS also wants to deepen Maria quite a bit. It keeps the core just far enough west to remain west of the colder pool of Jose's upwelling. It also decreases shear over the next few days, improving upper level support as it bends 300-200mb flow back NW over the Southeast interior.

18z GFS gets Maria's core closer to the Outer Banks than any of its previous operational runs. Probably static, but still worth noting.

Impressive..

00z ECMWF is coming west and closer to OBX. That in itself is important. Maria comes close enough to create some excitement. But the pattern looks less than favorable for an intense system. Going on track alone, the threat is increased. But to be optimistic, the hurricane itself is significantly weaker in that environment. We have to take the shift west seriously however.

The MLC may have tilted, but it did not decouple. Decoupling would have resulted in an entirely different looking satellite presentation.

Maria's forward motion has slowed down significantly over the past nine hours. Combined with the last two recon fixes and satellite, it has essentially been drifting to the NW. The core of Maria is currently positioned in a weak steering flow. Tonight is game time with regards to how steering flow will develop. I honestly don't have a clue how this will play out. I still think the core ends up east of the CONUS, but the slow down will definitely have an impact on modeling.

I think tonight's ECMWF op and the EPS is going to be the most important modeling yet with respect to knowing just how much of a real threat has developed with regards to the Carolina Outer Banks. Jose is rapidly filling IRL and we have the upper weakness developing over Florida. I really want to see how the ECMWF and its ensembles handle this before I would start getting concerned.

Fortunately, what you are seeing is overflow into the spillway, as designed. The dam has not yet failed. However, strong current is eroding and undercutting into the earthen dam at the bottom of the spillway. Therefore, the threat of failure does exist beyond the already dangerous situation of flooding due to uncontrolled release.

Those are storms in association with the upper low developing over the SE and Florida. Can it affect Maria? Absolutely. However, it needs to retrograde SW to have a significant impact on how much longitude Maria can obtain with respect to the SE coast. Ideally, it would be more influential if it was deeper and had a better presence in the 500 mb layer as it retrograded SW. But in any event, it is there in the 300-200 mb layer. It is the flow around that feature that has assisted in some periods of 10-20 kts of south-southwesterly shear over Maria today. But it is that feature and any rebuilding of heights NE of Maria that may draw it in closer to the N. Carolina coast. If that indeed happens.

The only good example I can think of at the moment that compares is Hurricane Gilbert's wind swath across the entire Jamaican landmass. Maria may end up worse, but I dare say the overall building codes in Puerto Rico were better with respect to both landfalls, though obviously still a lot of substandard construction exists in places. Ironically, a lot of the poorer areas of construction standards are in areas nearto San Juan. A lot of the structures I am seeing in SE PR look like well-built middle-to-upper class homes. Still there are pockets of immense structural damage in the aeriel footage posted earlier. And we should not forget areas on the NW side of PR with respect to wind damage. I have yet to see any aerial footage there and they were in the southwest and southern quadrant for quite a while. I should note this discussion with respect to a large population over a large area of a single landmass. Obviously, this is a different discussion entirely when incorporating the combined area/landmasses of the islands in the Lesser Antilles and Virgin Islands in regards to Irma's impacts. And the damage in Dominica by Maria looks as bad as the damage inflicted by Irma on Barbuda, Anguilla, St. Martin, etc.

USGS page for info about the watershed and dam: https://pr.water.usgs.gov/public/rt/pr_lakes/lake_50010800.html

Palmas Del Mar in the first video is a big wealthy resort area with very well-constructed concrete buildings, complexes and hotels. Not surprisingly, those structures faired well, but as the footage goes on you can see structural damage and deroofed houses. Yubacoa, Emajugua, Patallis, Arroya and the South Coast, you can definitely see the houses that faired better with good building codes. Still immense destruction. Levitown looks like a war zone, but again, you can see good building codes at work. Some well-built structures look severely damaged. Obviously, officials may need ground surveys to confirm codes, severity of structural damage, etc., but I have little doubt this was a Category 4 at landfall. The vast spread of extreme winds is impressive far inland. In retrospect, the ERC may have saved a small area near the coast from receiving catastrophic wind damage, but the larger eyewall took its toll.

Maria is still under a favorable 200mb pattern and the core is slowly moving away from Hispaniola. SSTs are still very condusive for intensification for the next 48-72 hours. I do not know if it will go though another period of significant deepening. That will have more bearing on the evolution of its internal structure. But it certainly won't be surprising.

Maria's ECMWF 96-144 hr positions would induce significant weakening. It's sitting right over a large cool pool of upwelling due to Jose's long duration stall last week. It's also in a southerly-to-southwesterly steering flow as the trough advances east. Maria would evolve into a large Jose-like storm besides. Really the next 48-72 hours of how the major features evolve is critical with regards to track and intensity. We simply need Jose's 500mb vort to get squashed and the WAR to not be so backed to the east. The odds of landfall just don't seem probable unless that occurs in rapid fashion.

Maria cleared out a huge symmetrical eye on IR.

That rain gauge in Caguas registering 35 inches of rain in 24 hours is insane. That is tucked in a valley surrounded by mountainous terrain. I can't even imagine; that's really nothing short of terrifying.

Maria's core has grown and expanded this evening. The old central vortex that passed over Puerto Rico is still easy to make out on shortwave, but appears devoid of heavy convection and looks to be weakening. It's probably going to take a while for the concentric intense convective banding producing current cold cloud tops to tighten up. That should get the core in a state conducive for any significant intensification. Right now the pressure and hurricane seems to be in a rather steady state. It also may need to gain some latitude from the Dominican Republic as close proximity can affect low-level inflow on the southern half of the circulation. Even if the larger eyewall/vortex tightens, Maria will probably have a large eye feature tomorrow.