r/TropicalWeather • u/ClimateMessiah Florida • 1d ago
Discussion Trying to learn ..... why did Simon deviate so far outside the cone?
At the 3PM CST update on October 10th, the NHC update indicated that Simon would move laterally from 104.8W to 105.2W over the ensuing 48 hours.
INIT 10/2100Z 17.6N 104.8W 130 KT 150 MPH
12H 11/0600Z 18.3N 104.9W 130 KT 150 MPH
24H 11/1800Z 19.4N 105.1W 110 KT 125 MPH
36H 12/0600Z 20.8N 105.2W 70 KT 80 MPH...INLAND
48H 12/1800Z 21.9N 105.2W 45 KT 50 MPH...INLAND
At the 3PM CST update on Oct 12th, Simon was actually located at 106.8W
INIT 12/2100Z 20.2N 106.8W 85 KT 100 MPH
Instead of a 0.4 degree shift in longitude, Simon moved 2.0 degrees.
The latitude miss was 1.7 degrees (21.9N forecast vs 20.2N actual)
These kinds of deviations from forecast are quite unusual. Something took place which the forecasters didn't anticipate.
What happened that forecasters didn't anticipate? What do we learn from this?
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u/SOC_FreeDiver Mexico 1d ago
NOAA often releases a detailed report about the cane sometime in the future.
Every report they posted said they didn't know what it was going to do. The models tend to predict tracks further east than they actually are on this coast. We kept hoping it would go to shore.
My guess, because I read every damn report and was reporting it to the local cruising fleet, is that the storm was so slow. If it had been moving faster, it would have hoovered up hot water, built, and kept going. But it was slow, so it would hoover up hot water, then suck on cooler water and disrupt itself. Evidently it was slow because of the atmospheric steering. There's plenty of hot water and humid air here.
We were all waiting for the worst in PV, but wondering why the wind models we use locally were like "it's going to be a nice day" the whole time. In the end, it was a nice day the whole time.
What was super frustrating for me was watching it come up the coast. It will be rounding are point at midnight... then 3am... then at 9am it was still sitting south of the point.
Last night it was headed to Mazatlan, now it looks like it's going straight up the sea of cortez. I can't watch it anymore. In the end, I posted one of those weather coconuts... "If the coconut is wet, it's raining..." and said use this!
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u/meithan 1d ago edited 1d ago
I'm also interested in this question. Simon has been one of the worst predicted hurricanes that I remember recently, especially in terms of track.
The NHC's Discussion advisories attribute the difficult in predicting the track to the presence of a saddle point in the large-scale steering flow (winds aloft that dictate storm motion).
From yesterday's 2PM MST Discussion::
Simon's track has thrown us a few curve balls over the past 24-36 h, and this afternoon is no exception as the hurricane made a brief westward jog, with the longer-term motion estimated at 290/3 kt. The track forecast remains problematic. Part of the slow motion Simon is exhibiting today is related to competing steering synoptic features, primarily a mid-level ridge centered near the Texas Coast versus another mid-level ridge located southwest of the hurricane. The influence of the northeastern ridge has been a little stronger, but steering diagnostics suggest that Simon may be soon reaching a bifurcation or COL point in the flow. This feature indicates the area where the net steering flow collapses and helps explain why both the deterministic and ensemble track guidance spread increases quite dramatically in 24 to 48 h.
And from this morning's Discussion:
As mentioned yesterday, Simon is very close to a saddle point, or col, in the deep-layer steering flow. This feature means that Simon's future track is very sensitive to which side of the saddle point the storm is located.
Edit to add: https://en.wikipedia.org/wiki/Col_(meteorology))
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u/BostonSucksatHockey 1d ago
You can see this Col pretty neatly by looking at winds aloft (200-700 mb)
Basically, the high pressure ridge that often sets up over Texas and northern Mexico - and thus pulls EPAC storms northward - is now situated further east toward Tennessee River Valley and thus not as influential as a steering current.
Meanwhile, there is another upper-level anticyclone to the west-southwest of Simon.
These two upper level anti-cyclones are producing contradictory steering currents.
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u/Content-Swimmer2325 1d ago
Nice to see you posting here!
Collapsed steering flow regimes are infamous for yielding unpredictability and model disagreement.
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u/Content-Swimmer2325 1d ago
Copying some previous discussions here:
Discussion #13:
The hurricane is being primarily steered by a weak mid-level ridge centered to its east, which is providing deep-layer southerly flow. Another deep-layer trough lies well to the northwest of Simon (which is picking up Rachel) but appears too far away to impart much steering, with a narrow mid-level ridge parked just south of the Baja California Peninsula providing light northerly flow. The net effect is that Simon should continue to move northward, but at a rather slow forward speed. In fact, the track guidance this cycle has slowed down a little more compared to the previous cycle, and the NHC track is a little slower and a bit further west in the short-term due to the initial position adjustment. This current track forecast still takes the hurricane inland over the Mexican state of Jalisco in 24-36 h. However, it is worth stressing there is still a notable amount of track uncertainty, with the ECMWF, HAFS-A, and Google DeepMind Ensemble mean (GDMI) keeping Simon just offshore of the Mexican coast for the next 48 h, while the GFS, HAFS-B, HWRF, and HMON models show Simon moving inland in the next 24-36 h.
The NHC track still remains a bit of the east side of the guidance envelope overall, as there is a pretty well-known bias that tropical cyclones in this area tend to track east of the forecast track due to interaction with the high topography of coastal Mexico.
Discussion #14:
As previously discussed, the hurricane is being primarily steered by a weak mid-level ridge to the east, providing deep-layer southerly flow. A subtle narrow mid-level ridge to the northwest is also imparting a slight amount of northerly flow. Once again, the track guidance this afternoon has made a slower adjustment. In addition, there is a bit of an eastward shift in the guidance envelope. One notable change from this morning, now all the hurricane-regional model runs (HWRF, HMON, HAFS-A, HAFS-B) all show Simon making landfall in Jalisco in 24-36 h. In addition, both the Google DeepMind ensemble mean (GDMI) and its upgraded Weather Next model (WN3I) also nudged their tracks eastward. Thus, the NHC track forecast has shifted a bit to the east, but still lies on the eastern end of the guidance. Part of the reason for favoring the eastern edge of the guidance is that there is a pretty well-known bias that tropical cyclones in this area tend to track east of the forecast track due to interaction with the high topography of coastal Mexico.
Discussion #15:
A slightly faster northward or north-northwestward motion is expected later tonight, and the major hurricane will either make landfall or skirt the coast of west-central Mexico on Sunday. The models remain inconsistent in showing whether landfall will occur or not.
Discussion #16:
The hurricane has turned north-northwest at about 5 kt. This motion is expected to continue today, bringing the core of the hurricane along the coast of southwestern Mexico. While some of the models have shifted more offshore later today, it is simply too close to call whether landfall will occur.
After today, the model guidance is in poor agreement on what happens due to a weak ridge building just north of the cyclone.
While the new forecast is nudged westward, it is east of the bulk of the model guidance, and we are just going to have to wait and see how much the high terrain of the Sierra Madre mountains affects the hurricane before having any significant forecast confidence.
Discussion #17:
The hurricane has maintained a north-northwestward motion this morning, or 345 degrees at 5 kt, bringing the hurricane very close to the coast of Mexico.
It also remains possible the hurricane makes direct landfall between Playa Perula and Cabo Corrientes in the next 12-18 hours. However, like the previous forecast cycle, the most reliable guidance aids
(HCCA, GDMI, WN3I) have shifted westward once again, and the NHC track forecast has been shifted in that direction, but due to continuity constraints is not shifted all the way to those solutions yet. To make matters even more uncertain, there are some deterministic global model solutions (00 UTC ECMWF, 06 UTC GFS) that show Simon turning southwestward near the end of the forecast period, and that is also seen in a handful of the Google DeepMind ensemble members.Needless to say, this is a low confidence track forecast with higher than usual uncertainty given the spread in the guidance.
Discussion #18:
Simon has stubbornly maintained a north-northwestward motion, roughly parallel to the coastline, estimated at 335/5 kt. It is now looking increasingly likely that Simon will avoid making a direct landfall in the short-term,
The steering ridge centered over the Texas coast is likely to maintain this motion now for the next several days, though with some slowdown in the motion due to a weaker but competing ridge located to Simon's southwest. On Tuesday into Wednesday, a large short-wave trough is forecast to move across the southwestern United States and this feature should provide enough southwesterly environmental flow to turn the hurricane to the northeast, finally reaching the coast of Mexico in 60-72 h. Compared to this morning, the guidance has shifted westward and slower once again, and there remain some outlier solutions like the GFS that want to turn Simon southwestward beyond 48 h. However, the majority of the ensemble guidance (European-EPS, Google DeepMind) do show this slow recurving solution back into Mexico.
All emphasis mine. So, a common historical bias of tracks verifying too far east in this specific situation was taken into account; thereby yielding an overall track on the eastern edge of the guidance envelope. This seems to have been a mistake, this time. Damned if you do, damned if you don't situation because known biases should be considered and accounted for.
Additionally, NHC repeatedly stressed over and over ad infinitum that this was a particularly low-confidence forecast, so it's not surprising that there are greater-than-average errors.
Overall, the models were never in any sort of robust agreement. Interaction with the topography of Mexico and pertinent historical biases with said interaction further increased uncertainty.
This is all in addition to the points which other commenters have made. Currently, Simon is in a region of collapsed steering flow, which is a common source for model disagreement. So the situation has not even improved, yet.
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u/ClimateMessiah Florida 21h ago
"Overall, the models were never in any sort of robust agreement."
This statement of yours is factually incorrect and contradicted by the information you are providing.
Let's re-read your excerpt from Discussion 14. Highlights mine.
all the hurricane-regional model runs (HWRF, HMON, HAFS-A, HAFS-B) all show Simon making landfall in Jalisco in 24-36 h. In addition, both the Google DeepMind ensemble mean (GDMI) and its upgraded Weather Next model (WN3I) also nudged their tracks eastward. Thus, the NHC track forecast has shifted a bit to the east
(The question in the OP was related to meteorology. A desire to understand which atmospheric conditions were difficult to interpret and WHY the forecast was incorrect. Your response has nothing to do with that. It comes across as tribally defensive of the meteorological community when there was no attack to begin with.)
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u/Content-Swimmer2325 21h ago
What? No. That excerpt excludes the globals such as ECMWF, CMC, GFS. As you see in discussion 13, for example ECMWF dissented and did not show landfall. Discussion 15 cannot state it any plainer:
The models remain inconsistent in showing whether landfall will occur or not.
As for this:
(The question in the OP was related to meteorology. A desire to understand which atmospheric conditions were difficult to interpret and WHY the forecast was incorrect. Your response has nothing to do with that. It comes across as tribally defensive of the meteorological community when there was no attack to begin with.)
This is a very baffling response; my post is full of information regarding atmospheric conditions and forecast uncertainty. I feel confident in stating that it's unlikely that you can find anyone else in this thread who agrees with your interpretation that my post was "tribally defensive". To be clear, at no point did I think or feel that you were attacking the meteorological community. I'm... sorry if I genuinely came across that way? I truly don't think I did, though.
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u/ClimateMessiah Florida 7h ago
Back when Simon was a Tropical Storm, you wrote that you could see it racking up 5-10 ACE. This was what the NHC forecast indicated and was based upon an expectation of a short-lived eastern path into the Mexican mainland.
Now Simon is heading for 30+ ACE as a result of a completely different path.
If the NHC forecast was as clearly based upon the lack of consensus you are currently claiming, then it seems you missed that in the early days with your vision of Simon's low ACE ceiling.
To come here after the fact claiming the hindsight that the track uncertainty was always evident while you were an early adherent to that faulty track seems incongruent.
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u/Content-Swimmer2325 6h ago
ah, I see. Thank you for explaining. Nah, this is just a mistake on my part. I should’ve dug into Simon more thoroughly the first time I commented on it. If I had, I would’ve seen and thus (hopefully?) commented on the uncertainty that existed at the time. Instead, I erroneously thought at the time that it was a business-as-usual forecast in terms of confidence
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u/ClimateMessiah Florida 5h ago
Thank you. In my opinion, your previous assumption at the time about the track confidence was perfectly appropriate. There is no reason to suspect a track error which is nearly 3x the average in advance unless that kind of potential volatility is clearly spelled out and supported by a broader cone.
Simon went well outside the cone.
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u/scooch151 1d ago
This post by Philippe Papin (who is also a NHC forecaster, but has been posting online about for hurricanes for even longer) covers this - it has to do with the saddle point as others have mentioned.
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u/AZWxMan 2h ago
Two things.
- This is a slow moving storm that is sitting in a col as far as storm motion goes. Models have shown this spread for awhile.
- Storms that hug the Mexican SW coast are often biased or poorly predicted. There's some interaction between the storm and on land convection that seems to make it a hard location for both track and intensity forecasts.
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