Hurricane Hurricane IDALIA: threat to the northeastern Gulf Coast

[Casuarina Head]

Now that the system in the northwestern Caribbean has been designated, I have decided to begin the main thread on the potential threat to land.

While no model currently goes much beyond a high-end Category 1 at most, the similarities with a number of recent storms (most notoriously Michael, which was not modelled as particularly strong at first) are striking. The latest GFS, many EC ensembles, the Canadian model, and the ICON all indicate the potential for rapid nearshore deepening within a day of landfall on the northeastern Gulf Coast. In particular models suggest a strongly divergent upper-air pattern, with hints of dual outflow, that would favour potentially rapid strengthening within 18–24h of landfall. We have seen plenty of similar examples in the Gulf since 2016. Furthermore, during El Niño storms tend to intensify closer to North America, rather than in the Caribbean and MDR, which tend to be more unfavourable than the subtropics.

I think there is ample reason to be concerned. I expect models to adjust upward, potentially on rather short notice. Climatology indicates the threat for a strong hurricane.

 

[Casuarina Head]

One potential factor that could limit intensification yet is not being mentioned: the absence of a moist, southerly inflow-jet. Historically powerful systems that rapidly deepened just prior to landfall on the Gulf Coast exhibited moist inflow from the Caribbean. For example, satellite-derived imagery of Camille and Eloise showed this. In 93L’s case, however, the persistence of shortwave ridging between it and Franklin will result in subsidence over the Caribbean, which is forecast to persist over the next five days. So 93L’s eastern flank will continue to ingest unusually stable air from the Caribbean. (The same characteristic was noted in relation to Michael, interestingly.) Even though this will not prevent intensification, it might mean that 93L’s peak winds may not translate as well to the surface as expected. We could easily see a MSLP in the low 900s yet see lower 1-min, 10-m winds than normally seen at such a value. Also, most models do not suggest that 93L will be much larger than average in size, which, along with the aforementioned factor, would probably reduce the potential storm-surge somewhat.

 

[JBishopwx]

 

[Taylor Campbell]

At this time- I side with the CMA, and EURO 2-day consistency landfall point of somewhere between Ozello, FL and Alligator Point, FL as a category 1, potentially category 2 hurricane. I expect landfall to be the morning of Wednesday, August 30th closest to the Fish Creek, Jena, Horseshoe Beach, FL area.

 

[Casuarina Head]

At this time- I am siding with the CMA, and EURO 2-day consistency landfall point of somewhere between Ozello, FL and Alligator Point, FL as a category 1, potentially category 2 hurricane. I expect landfall to be the morning of Wednesday, August 30th closest to the Fish Creek, Jena, Horseshoe Beach, FL area.

Based on the latest trends, hurricane-status might be generous, or at least somewhat questionable. The latest EC and GFS in particular are showing more constricted outflow shortly prior to landfall than previous runs did. The upper-level anticyclone appears to be smaller and more elongated as well. Maybe a strong tropical storm or low-end Category 1 is more likely than a borderline-Category-1/-2 system. I’m not convinced that the hazards (e.g., rain and storm-surge) will be especially great, owing to dry-air intrusion, a relatively compact circulation, and a fairly rapid forward speed. I think that models will shift eastward over time and converge on a landfall between Hernando Beach and the mouth of the Suwannee River. As far as intensity is concerned, I would anticipate a moderate to strong tropical storm.

 

[JBishopwx]

Much healthier this morning compared to the models. I expect we get advisories later today.

 

[OHWX97]

These last two hurricane seasons have me feeling uneasy about a potential "I" named storm in the Gulf of Mexico this time of year. I'm not trying to say future Idalia will end up anywhere near as strong or destructive as Ida or Ian, but never underestimate a favorable gulf during peak season.

 

[Casuarina Head]

00z Euro Ensemble showing my dream back on April 23rd of a category 5 in the Gulf.

Before you say that's just a dream, I dreamed 10 years ago about the EF3 that hit Amory MS this past March. Few years prior to the Smithville MS EF5 tornado on April 27th 2011, I dreamed about a tornado going right in front of my house in Smithville on hwy 25 North. I lived right off the highway. Literally right in front of it.

Eastern Gulf with just west of Mobile towards Tallahassee in the threat zone.

@JPWX Remember your dream about a 900-mb hurricane making landfall between Mobile and Tallahassee? There’s also this:

Wed 16 August 2023 7:11, UK The very first prediction in the claims, the “first-ever Category 6 Hurricane” will occur on September 4, 2023. ... The time traveler claims that the terrifying hurricane will run up “almost the entire U.S. East Coast”, but it will “mainly affect Florida and both Carolinas.”

Aside from the date, everything else seemingly matches the latest projections, including a track from northwestern Florida to the Carolinas. Some of the dynamical guidance is now showing MSLPS in the 930s mb. A Category-4+ system into Tallahassee would be unprecedented, though at this point I am still quite skeptical. Without ample moisture from the Caribbean, prospective Idalia will be less likely to become very strong, much less maintain intensity up until landfall, at least in terms of surface-based winds.

These last two hurricane seasons have me feeling uneasy about a potential "I" named storm in the Gulf of Mexico this time of year. I'm not trying to say future Idalia will end up anywhere near as strong or destructive as Ida or Ian, but never underestimate a favorable gulf during peak season.

@OHWX97 “Idalia” incorporates Ida, incidentally.

 

[Clancy]

NHC saying it will start initiating advisories on 93L this afternoon.

1. Northwestern Caribbean Sea and Eastern Gulf of Mexico (AL93):
Showers and thunderstorms associated with an area of low pressure
located near the Yucatan Channel continue to gradually become
better organized. If this trend continues, advisories will be
initiated on this system later today. The system is expected to
move very slowly northward into the southeastern Gulf of Mexico
during the next couple of days. Heavy rains are likely over
portions of western Cuba and the Yucatan Peninsula of Mexico.
Interests in the Yucatan Peninsula of Mexico, western Cuba, and
Florida should monitor the progress of this system.
* Formation chance through 48 hours...high...90 percent.
* Formation chance through 7 days...high...90 percent.

 

[Clancy]

18Z spaghetti models shifted a bit westward.

 

[Taylor Campbell]

@JPWX Remember your dream about a 900-mb hurricane making landfall between Mobile and Tallahassee? There’s also this:

Aside from the date, everything else seemingly matches the latest projections, including a track from northwestern Florida to the Carolinas. Some of the dynamical guidance is now showing MSLPS in the 930s mb. A Category-4+ system into Tallahassee would be unprecedented, though at this point I am still quite skeptical. Without ample moisture from the Caribbean, prospective Idalia will be less likely to become very strong, much less maintain intensity up until landfall, at least in terms of surface-based winds.

@OHWX97 “Idalia” incorporates Ida, incidentally.

@Casuarina Head, what shows 930s?

 

[OHWX97]

 

[Taylor Campbell]

NHC gets excited when their new models forecast CAT 3. LOL.

 

[Casuarina Head]

Above: differences between the setups at the times of Camille (1969, top) and soon-to-be-Idalia (2023, bottom). The following details are noted:

• Camille did not have to contend with a tropical system to its northeast, unlike Idalia-to-be. In 1969 Hurricane Debbie was consistently sited to Camille’s southeast, whereas in 2023 Franklin will be northeast of Idalia-to-be. This affects the placement of shortwave ridging on the eastern flanks of these respective storms, over the western North Atlantic (Sargasso Sea).
• Ridging will be displaced farther south in relation to Idalia than Camille, resulting in increased subsidence and drier air over the Caribbean. Its placement also will prevent a strong southerly inflow from developing, unlike in 1969. This, in turn, will likely limit the potential for Idalia’s strongest winds to effectively mix down to the surface.
• Higher background pressures and surrounding dry air, in turn, mean that Idalia will likely be a fairly small system, reducing the risk of widespread, large storm-surge. Additionally, the dry air and steady translational movement imply that heavy rainfall should not pose much of a threat.
• Idalia’s outflow in the western quadrant is likely to be restricted by the trough, suggesting westerly shear.

Bottom line: even if Idalia’s MSLP enters the low 900s mb, its actual winds, surge, and rainfall may be less impactful than expected for a storm of its intensity.

930s? What are you talking about?

@Taylor Campbell The latest HAFS-A/-B and HWRF runs forecast MSLPS ranging from the low 930s to the low 940s mb.

 

[Casuarina Head]

^ @Taylor Campbell

 

[JPWX]

My two cents on this: given the hurricane models are all showing rapid intensification, it'll be tracking over the warmest Gulf waters, and the fact that we've had numerous examples of rapid feedback up to landfall just to name a few (Michael, Ida, Ian, Sally, Laura, Delta) during the last 5 years. I love the fact too that this "time traveler" didn't see a "category 6" until August 16th when I dream about a 900mb Gulf system in April.

Great to know that this system won't be very impactful as well. I'm sure the NHC will take that into consideration.

 

[Taylor Campbell]

@Casuarina Head, okay thank you for sharing that model information. I saw that a few tropical intensity models on the 18z run showed Cat 3, but didn’t know of the pressures in the 930s. I’ve seen several GFS ensembles in the 960s, 970s, and the lowest Global operational runs from time to time show MSLP around 970mb. If this system undergoes rapid intensification into that range, I could see it actually be lower than that number in the future.

 

[JBishopwx]

Think Mike Weather Page has been the only one who has mentioned it, but we are going to have some major surge issues because of the supermoon next week.

 

[Casuarina Head]

Great to know that this system won't be very impactful as well. I'm sure the NHC will take that into consideration.

@JPWX I said that it might be “less impactful than expected” relative to its intensity (pressure). I think that this system could easily get close to 900 mb over the Gulf yet feature a) maximum sustained winds of at most Category-3 status at the surface and b) storm-surge values that are closer to those of a Category-3 than a Category-4+ system. The main forces that will facilitate intensification in this case are a) nontropical in nature—i.e., the trough—and b) the thermodynamic profile of the Gulf itself (very warm SSTA and high oceanic heat content). To generate sustained Category-4+ winds at standard elevation near the northern Gulf Coast, a storm would need a reservoir of moisture from the Caribbean and well-developed dual outflow. Storms like Camille and Eloise featured both. In this case Idalia will have neither, as illustrated previously. I will point out that Michael also lacked these features, and a reliable survey indicated that peak gusts on the shoreline only reached ~130 kt, which would suggest maximum sustained winds of about 100 kt, making Michael a marginal Category 3 on land—consistent with nearby observations (even though the MSLP was on the order of 916–9 mb). So I think Idalia could feature a Cat-5 MSLP yet only Cat-3 winds and surge, along with relatively minimal rainfall. Nevertheless, even a low-end Cat-3 is still a major hurricane and should be taken very seriously.

 

[UncleJuJu98]

Think Mike Weather Page has been the only one who has mentioned it, but we are going to have some major surge issues because of the supermoon next week.

Yikes I've read of some hurricanes in the past that have hit I think there's one in the northeast during a lunar phase that really exacerbated flooding.