Alrighty, before we delve into Gustav just a quick blurb about me so that you know I'm not just some shmoe throwing around bad info. I'm a professional meteorologist working as a forecaster with a focus on Atlantic tropical cyclones and Eastern U.S. temperatures. Been doing hurricane forecasting for about 16 years (ugh, that makes me feel old!). So, without further ado, on to Gustav...
First a couple of quick-hit points:
- I'll talk about Hanna a bit, with regard to what some of the longer term "global models" are doing with that storm, but the focus will be on Gustav.
- The diary title says "Hurricane" Gustav. To be clear, Gustav is a tropical storm right now, not a hurricane. However, as I write this Friday morning, he's (okay, forgive the male pronouns - some of you get bothered by that... sorry, it's just natural for me to refer to Gustav as "he" ...and Hanna as "she" for that matter) just coming offshore of Jamaica, and the satellite presentation is already improving. Moreover, 100% of the data supports intensification. So, Gustav should be back up to a hurricane soon, and his eventual threat to the U.S. is likely to be at hurricane status.
Okay, let's start with the current status. Aircraft reconnaissance data indicates a minimum central pressure of 988mb, with maximum flight level winds of 54kts. Due to their actual flight level (conversion to estimate surface winds depends on how high the plane is flying), this indicates that Gustav is a 50-55kt tropical storm. He was at 60kts yesterday. The central pressure verifies this trend. Gustav was down to 983mb yesterday (lower = stronger). A 5mb change in a day isn't huge; so, this means minor weakening. So, again, 50-55kts seems reasonable. And, indeed, that's what the National Hurricane Center has. Their 8AM Intermediate Advisory has Gustav as a 65mph storm (that's about 55kts).
Looking at the current satellite imagery shows that Gustav is improving in organization. Here's a current snapshot of him, as of 8AM EDT:
...you can see from this image that the convection (deep reds) is not tremendous around his center (near western Jamaica). But a loop of this imagery does show improving organization this morning. So, Gustav will likely get to hurricane strength later today. And Gustav will be aided by very warm water temperatures:
...the necessary temperature for sustaining a hurricane is 26 degrees Celcius. Western Jamaica, where Gustav is as I write this, is just off the southeast corner of this image; and he's moving west-northwest and will turn northwest through the Yucatan Channel (the water between Cuba and Mexico) or across far western Cuba. Those water temperatures are all between 29 and 33C. Anything over 30C is ridiculously warm. The lone positive here is that you may notice that the temps do cool a bit closer to the U.S. And the depth of the warmth is also important - and it is shallower near the U.S. In fact, a heat potential map - found here - shows some pretty low heat potential in the northern Gulf. On the flip side, unfortunately it takes time for storms to spin down, and that heat potential map is somewhat misleadingly low in the northern Gulf. So, there's plenty of support off the TX/LA/MS/AL/FL coasts for a major storm... but at least the worst of the worst storms (a Category 5) would not be supported.
Okay, so what about the forecast? Well, unfortunately, the forecast model guidance should be coming into agreement as we close in time-wise. But it's not. Nonetheless, they are still reasonably clustered. So, there continues to be fair confidence - for a four day forecast - as to where Gustav is headed. Here's a look at the latest model tracks:
...there are a few lines bending to the west towards Texas now. And at least one of these (the blue EGRI line) isn't just some trash model. Yes, there are some computer models that aren't worth the CPU cycles they waste. The EGRI (known more commonly as the UKMET ...the United Kingdom Meteorological office's model) isn't one of those. It's not the best of models, but it performs surprisingly well on tropical cyclones. Though it was terrible in 2006, as you can see at this link it tends to be among the better models. So, this westward bend is somewhat disconcerting. Nonetheless, it's an outlier. Most of the other models are focused between Mobile, AL and central Louisiana. Some updates on these models have recently come in, but for which an updated map isn't available. And I can report the the easternmost tracks, towards Mobile (from the GFDL and GFS models) have shifted westward more towards New Orleans.
...so, though there is more spread this morning - primarily due to a few westward outlier - the focus is unchanged. My thought yesterday was Morgan City, LA landfall in the wee hours Tuesday morning. That remains my thinking.
As for the intensity... well... here are the latest models:
...again, some brand new model data in suggests a weaker landfall. One new model has a Cat 3, the other a borderline 2 or 3. However, these same two models (the HWRF and GFDL) came in with some of their strongest forecasts to date (at landfall anyway) in their previous run. So, there is increasing inconsistency and increasing spread. As a forecaster, this is a little frustrating. Nonetheless, if you look at the image above, there does remain at least some solid agreement. First off, ignore the bottom cluster of lines. Those are from global models which do not handle hurricanes. Second of all, ignore the sharp dropoffs on some models after 84 hours (three and a half days ...late Monday); this is caused by landfall (once inland, Gustav will obviously weaken). Doing that, you can see that all of the models are between 90kts and 110kts at landfall. The breakpoint for Category 3 is 100kts. So, these models are showing a strong Cat 2 or a weak Cat 3.
Personally, I'm favoring a Category 3 scenario. I'm not an alarmist, so I'm doing so with reason. First, looking again at that model graphic, the GHMI and HWFI models are the two with the most superior ocean-atmosphere modeling capabilities. And they are both on the high end of the forecast. Second, these are just models. And I believe they are seriously suspect in their intensities in the 48-72 hour range. In that period, the GFDL (GHMI) and HWRF (HWFI) are in the 95-105kt range. I would seriously expect Gustav to be stronger than that. I believe Gustav will be in the 110 to 125kt range at that point. That does not necessarily translate to a major difference in the landfall intensity. But it could have a small impact. So, I'd lean to the high end of the model guidance... in the 100-110kt range for landfall intensity.
That's really about it for now. Lots of new data/info, but no real change to the forecast from yesterday. The threat range remains the same (upper Texas coast to western Florida Panhandle), with the focus also the same... around central or eastern Louisiana... likely landfalling roughly around the wee hours Tuesday morning... and best bet is that it's just over the threshold for a Category 3. Of course, I must again emphasize, this is four days away. Day 4 hurricane forecasts are typically NOT very good. Now, given the pretty decent model agreement, the Gustav forecasts may be fairly close. But they won't be exact. So, everyone in the threat region should be paying extremely close attention, and initial preparations should be well underway, with more serious preparations at the forefront of your mind. Check out the National Hurricane Center's Family Disaster Plan for some good info on how to prepare.
A brief word on Hanna, as promised... Global models are all over the place. The European model (ECMWF) brings Hanna to near Mobile, AL late next week or next weekend. The American model (GFS) is further east, towards the Florida Panhandle. The United Kingdom model (UKMET) does not go out far enough to show landfall, but clearly threatens the Gulf of Mexico. The Navy model (NOGAPS) has landfall in GA/SC late next week. And the Canadian model (GGEM) traps Hanna in an upper low a captures her just off the Mid-Atlantic and Northeast coast. Needless to say, way, way, way too much doubt and uncertainty with Hanna. Let's just focus on Gustav for now.
Updates forthcoming as warranted...
UPDATE: 11AM EDT ...new National Hurricane Center forecast out. Not much change. Just a shade further east at landfall - pretty close to my expectation - and still predicting landfall as a borderline Category 3. Their predicted landfall time is Tuesday mid-morning. I would lean slightly earlier, but as I've said before, that's splitting hairs. And even with their forecast, the impacts would begin reaching the coast well before mid-morning. They have left Gustav as a 55kt tropical storm. This is "sketchy". He's clearly gotten better organized since coming off of Jamaica. Radar from Pilon, Cuba (see below), even shows signs of an eye developing:
There is also some evidence of this, albeit less obvious, on satellite imagery.
...NHC should certainly not have upgraded Gustav to a hurricane yet. He's only just off of Jamaica and there are no "real" observations from reconnaissance aircraft at this time (a place is en route or will be shortly ...should arrive around 1PM or so). But they should have at least hedged a bit and took him up to 60kts (70mph). Once again, I'm probably splitting hairs - they can get this all ironed out once the plane gets there. But it seems like they should make the adjustment for what is most obviously occurring.
Not a whole lot of other new data. No new recon data, as noted. And most model data begins flowing in over the next few hours. 12Z short range American model (called the NAM) is in. It is historically atrocious with tropical cyclones. Largely not even worth the mention. But, since it looks reasonable, I'll just tell you that it aims for landfall sometime Tuesday in southeastern Louisiana.
In answer to "Alex with an E"'s question in the comments below... There is great debate over what would constitute a critical "strike" on New Orleans. Is NHC's track or my track about 50 miles west of New Orleans too far away from them to be destructive? Well, that does, of course, depend on a ton of things... size of the storm, intensity of the storm, and, frankly, infrastructure quality (i.e., levees not fully up to snuff since Katrina). So, it is difficult to answer precisely. But let's just use the National Hurricane Center's wind radii forecast and assume we need, roughly, 100mph winds (85kts ...or Category 2 force) to create severe conditions at New Orleans. The National Hurricane Center's forecast track places Gustav, at landfall, approximately 35-50 miles southwest of New Orleans. They do not issue wind radii at that time period (day 4). However, at day 3, when Gustav is nearly that same intensity, the radius of 50kt winds to the northeast is 90 nautical miles. They do not provide 100mph wind radii. But applying some simple math to, and assuming the same storm structure as the 36hr forecast, we can estimate the 64kt (74mph) winds to stretch out about 35 miles to the northeast. So..... that just about reaches New Orleans. In other words, they would be in the minimal hurricane force winds. This would not likely cause destructive damage. On the other hand, this is extremely, dangerously close. IF this forecasts holds, New Orleans would need to make FULL preparations and evacuations. But, IF this forecast is absolutely, 100% perfect (and it won't be!), New Orleans would escape major destruction... barely.
UPDATEx2 2:30PM EDT ...possibly my last update of the day, as I'm going away for the weekend. I will try to post each morning over the weekend, but please forgive me if I can't... it'll be tricky - I'll be busy and on dial-up (yes, I said dial-up!! ...egads!). Anyway, lots more info to digest right now, though still not much change in the bottom line...
A reconnaissance aircraft fix put Gustav at 984mb. That's back down 4mb since emerging from the Jamaican coast. So, Gustav is clearly intensifying, but not rapidly. Winds, estimated visually, were 57kts (65mph) at the surface; their onboard instrumentation (called SMFR) reported essentially the same thing. So, Gustav appears to be in the 55-60kt (60-70mph) range. Since the recon may not have sampled the "best" quadrant yet, I'd estimate that he's on the high side of this range... around 60kts. The continued appearance of a ragged eye:
...also support the notion that Gustav is very close to hurricane strength (65kts/75mph). So, 60kts (70mph) seems a good estimate to me.
Lots of new model data in, too. And some continued convergence, but it's not unanimous. For example, the HWRF - one of the "good" hurricane models - now stalls Gustav offshore. This would be good news (except for oil and natural gas production), as the "stall" takes place far enough offshore to keep most of the serious weather offshore. Louisiana would see some heavy surf, showers, and breezy conditions along the coast, but nothing serious. Meanwhile, the United Kingdom and Navy models, which were anomalies to the west last time have converged some towards the rest of the solutions (towards Louisiana). But neither of them are quite there... both have landfall near Galveston, TX on Wednesday (later landfall than it would be in Louisiana because it's further away). The Canadian model has also converged. It has dropped its strange "wandering" track and now just sends Gustav straight to New Orleans by Monday night. The new American model (the GFS) and GFDL model are similar to previous tracks... towards central (GFS) or eastern (GFDL) Louisiana. The GFS may be a shade west of previous runs. The newest European model is coming in as I write this. It appears to have shifted west slightly... showing landfall in western Louisiana very late Monday night.
So, all in all, the models continue to show some disagreement, but have converged a bit. They have also shifted slightly west and slightly earlier (both changes for the same reason... a stronger "ridge" will force Gustav further west, and provide stronger steering for a faster motion to the coast). The one outlier is the HWRF... while the consensus is slightly faster, the HWRF now stalls Gustav. So, I'd disregard that. My previously discussed landfall is still pretty close to the center of this range of predictions (maybe very slightly on the east side now), so I see no reason to change it... Morgan City, LA in the wee hours Tue AM.
Also as I write this, the 2PM NHC intermediate advisory has come out. They've upped Gustav to 60kts (70mph). That's a good call, in my opinion.
I guess that's about it. In case I can't update again (but I will try), please stay informed and be prepared!
UPDATEx3 3:15PM EDT ...Quickie update! Reconnaissance aircraft (that link updates automagically - so my apologies if you don't see the message to which I'm referring if you click on it) has reported 69kt flight level winds. Based on the "reduction" to surface (actually, at their flight level, the surface estimate would be an addition), the surface wind estimate is in the 70-75kt (80-85mph) range. This agrees very well with their on-board instrument (SFMR = Stepped Frequency Microwave Radiometer), which is estimating surface winds at 79kts (90mph). Also, the recon picked up a surface pressure of 984mb. Note the 41kt winds at the point of that report. That means they weren't at the center. So, the central pressure is below 984mb. So, Gustav is stronger.
...in short, Gustav is almost certainly now a hurricane. I don't have E.S.P. with the National Hurricane Center. I can't tell you that they will upgrade Gustav on their 5PM EDT official update. But I can tell you that they probably will... and they should. Gustav UNofficially, is now a 70kt (80mph) Category 1 hurricane.
UPDATEx4 3:20PM EDT ...Okay, it's official. Hurricane Gustav. 65kts (75mph), according to NHC. Frankly, they should've gone to 70kts (80mph)... but that's splitting hairs again... whatever, it's a hurricane.
And recon now reporting 978.4mb central pressure. A significant drop in a short time. Sometimes, these come in a bit low. The official fix may be 979 or 980. Still a good drop - four milibars, at least - in less than two hours. So, further immediate intensification is likely (wind increases usually lag the pressure drop).
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