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WxWatcher007

Major Hurricane Laura

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Again...you really need a fully developed eyewall for true RI....we don't have that quite yet...

 Most of the models last few rus have had hinted at the RI window, late this eve. through tomorrow morning. And that is still my thinking.

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15 minutes ago, wncsnow said:

So your forecast is for cat 2 at landfall? I think she has more going for her than against her. I don't think there will be much weakening near landfall. Today's Euro kept her intensifying right up until then. 

NHC has 100 kt near landfall  I said strong Cat 2, so that's 95 kt.  That's not that far off really.  Also, I said. "difficult to get anything higher than a strong Cat 2".  I didn't say it was impossible.

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Just now, LakeEffectKing said:

Again...you really need a fully developed eyewall for true RI....we don't have that quite yet...

 Most of the models last few rus have had hinted at the RI window, late this eve. through tomorrow morning. And that is still my thinking.

Exactly.  Get the eyewall established first before jumping to RI.

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5 minutes ago, vortex95 said:

Rapid very cloud top convective development in a blob fashion in one quad isn't generally a good sign overall for significant intensification. You want to see a smooth ring of convection gradually develop, and cool with time, and wrap around the center, and most importantly, persist for more than just a couple of hours.   At that point, RI is much more likely.

It is definitely wise to be cautious and conservative, but your posts seem to be too much on that end of the spectrum. Just relax and watch everything unfold, you're making so many definitive statements too early. A gradually strengthening Laura over the next 36 hours would still be equally menacing.

Pulsating convection (in a blob fashion) is typically an indication of a storm interacting with drier air in the mid-levels, but you do not need a well developed CDO for RI to commence. Storms can rapidly intensify from even tropical storm strength and would not have well defined ring CDOs. In addition, I'm not sure any particular met or model forecasted for RI during the day today, but rather a gradual improvement in structure before tomorrow morning when conditions are much more favorable. 

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Some nice VHTs going up with the overall presentation morphing from an embryo-like (dominant single band) towards partial ring. Dare I say the tilt that was apparent earlier this morning is probably close to resolving. Upstream dropsondes earlier did show a *bit* of dry air, but nothing particularly worrisome with shear on the decline. PWATs generally running >1.8" and DCAPE 900 or less. Concur on this evening being the beginning of the RI window at the pace of organizational improvement.

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12 minutes ago, vortex95 said:

Rapid very cloud top convective development in a blob fashion in one quad isn't generally a good sign overall for significant intensification. You want to see a smooth ring of convection gradually develop, and cool with time, and wrap around the center, and most importantly, persist for more than just a couple of hours.   At that point, RI is much more likely.

This logic is flawed.  You seem to state that you need good organization to get good organization.  But what you are failing to acknowledge is that there is a transitional time period between bad organization and good organization.

Not saying that RI is imminent or even that it will definitively happen, but just that it is irresponsible to throw in the towel based on ill-concieved notions.

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12 minutes ago, HKY_WX said:

I disagree w/ your premise that you cant have a Cat 3 or 4 with some mid-level dry air around. It's happened many times. Almost all major hurricanes that track north of 25 Latitude will likely face dry air problems. If we're talking about achieving  Cat 5/historical wind/pressures, sure I would agree the environment would need to be pristine.

Dry air is almost always an issue at some level even in the deep tropics.  It is matter of how widespread it is and its values, in addition to how strong and/or large a TC is.  We see fairly dry air both NE and NW of Laura now.  Dry air is more an issue for smaller systems that are trying to get established.  This is Laura right now..  If Laura was already an intense hurricane much more symmetric than it is now and larger, the current dry air around it likely would not be much of an issue.  So it isn't just the mere presence of dry air alone that affects a TC.

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Perhaps my use of the term “bombs away” is premature (also I love that term for tropical systems and nor’easters) but this is the structural development we need for that to occur. There does not seem to be anything (other than some modestly dry mid level air) that signals this isn’t the start of a significant (dare I say rapid) strengthening trend. The shear has clearly abated, the storm is becoming well-ventilated, and is now generating consistent enough convection to mix out dry air. It has to start somewhere and I believe Laura has the dynamite set and the fuse lit. I guess were arguing when that fuse reaches the explosives... 

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Don't know if this has already been posted.   It's experimental, but I already like it.

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Dry air is almost always an issue at some level even in the deep tropics.  It is matter of how widespread it is and its values, in addition to how strong and/or large a TC is.  We see fairly dry air both NE and NW of Laura now.  Dry air is more an issue for smaller systems that are trying to get established.  This is Laura right now..  If Laura was already an intense hurricane much more symmetric than it is now and larger, the current dry air around it likely would not be much of an issue.  So it isn't just the mere presence of dry air alone that affects a TC.

Shear due to the old remnant PV is becoming negligible. Diabetic heating is taking care of the rest. This isn't the same synoptic spread as the past few days. Also upper 200 hPa flow is reversing to become southeasterly. Therefore, we have nothing to advect the marginal mid level stable Theta-E into the vort until perhaps near the coast as some interior continental airmass subsidence might get on the SW side when a more southerly steering flow kicks in. That is not guaranteed however and its intrusion may not occur until well after landfall.
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It's easy to get lost in the details with all kinds of data that's readily available. Better to take a step back and assess in 3-6 hour increments. We've seen steady improvement in structure throughout the day, but shear and  dry air has impeded progress. As shear begins to relax this evening, we should see the system begin to mix out the dry air, and begin fairly significant intensification by early tommorow morning. 

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5 pm advisory

344 
WTNT43 KNHC 252040
TCDAT3

Hurricane Laura Discussion Number  24
NWS National Hurricane Center Miami FL       AL132020
400 PM CDT Tue Aug 25 2020

Satellite imagery shows some changes in the convective pattern of 
Laura since the last advisory.  The ragged central dense overcast 
seen earlier has been replaced by a curved convective band that 
wraps almost all the way around a cloud-filled banding-type eve. One 
possible reason for this change is that the imagery also suggests a 
tongue of dry air is trying to entrain into the cyclone just west of 
the central convection.  Aircraft data received after the last 
advisory did not show any fall in the central pressure, but did have 
high enough flight-level and SFMR winds to justify nudging the 
initial intensity up to 70 kt.

The initial motion is now west-northwestward or 300/15 kt.  There is 
no change in the forecast philosophy since the last advisory. The 
hurricane is currently on the south side of a large-deep layer ridge 
over the southeastern United States, and it is moving toward a break 
in the ridge caused by mid- to -upper-level troughing over Texas and 
the southern Great Plains.  The current and forecast synoptic 
pattern should steer Laura west-northwestward this evening, followed 
by a turn toward the northwest tonight and toward the north by 
Wednesday night and Thursday.  This will result in the hurricane 
making landfall in the area of southwestern Louisiana or the upper 
Texas coast late Wednesday night or Thursday morning. The new 
forecast track has a slight eastward nudge during the first 12-24 h, 
but the landfall position is almost unchanged from that of the 
previous forecast.  It should the be noted that the current forecast 
track lies to the east of the ECMWF and UKMET models, so it is still 
possible that the forecast track could nudge westward in later 
advisories.  After landfall, Laura is expected to recurve into the 
westerlies and move eastward through the Tennessee Valley and the 
mid-Atlantic States before reaching the Atlantic in about 120 h.

All indications are that the hurricane should steadily to rapidly 
intensify during the next 24 h, with the only negative factor being 
the possibility of more dry air entrainment.  The intensity forecast 
will go with the scenario that the dry air will not significantly 
hinder strengthening.  The global models are in good agreement that 
Laura will encounter increasing southwesterly shear in the last 6-12 
h before landfall, so the intensity forecast shows slower 
strengthening during that time.  With all that said, the landfall 
intensity of 100 kt is unchanged from the previous advisory.  After 
landfall, Laura should weaken through the 96 h point, followed by 
re-intensification through baroclinic energy as the cyclone becomes 
extratropical.

Users are again reminded not to focus on the exact details of the 
track or intensity forecasts as the average NHC track error at 36 h 
is around 60 miles and the average intensity error is close to 10 
mph. In addition, wind, storm surge, and rainfall hazards will 
extend far from the center.

Key Messages:

1. There is a danger of life-threatening storm surge with large and 
dangerous waves producing potentially catastrophic damage from San 
Luis Pass, Texas, to the Mouth of the Mississippi River, including 
areas inside the Port Arthur Hurricane Flood Protection system. This 
surge could penetrate up to 30 miles inland from the immediate 
coastline in southwestern Louisiana and far southeastern Texas.  
Actions to protect life and property should be rushed to completion 
this evening, as water levels will begin to rise on Wednesday. 

2. Hurricane-force winds are expected Wednesday night in the warning 
area from San Luis Pass, Texas, to west of Morgan City, Louisiana, 
and the strongest winds associated with Laura's eyewall will occur 
somewhere within this area. Hurricane-force winds and widespread 
damaging wind gusts are also expected to spread well inland into 
portions of eastern Texas and western Louisiana early Thursday.

3. The threat of widespread flash and urban flooding along with 
small streams overflowing their banks will increase due to heavy 
rainfall Wednesday night into Thursday from far eastern Texas, 
across Louisiana, and Arkansas.  This will also result in minor to 
isolated moderate river flooding.  The heavy rainfall threat will 
spread northeastward into the middle-Mississippi, lower Ohio and 
Tennessee Valleys Friday night and Saturday. 

FORECAST POSITIONS AND MAX WINDS

INIT  25/2100Z 24.7N  88.3W   70 KT  80 MPH
 12H  26/0600Z 25.7N  90.3W   85 KT 100 MPH
 24H  26/1800Z 27.5N  92.4W   95 KT 110 MPH
 36H  27/0600Z 29.7N  93.8W  100 KT 115 MPH...ON COAST
 48H  27/1800Z 32.2N  93.9W   65 KT  75 MPH...INLAND
 60H  28/0600Z 34.7N  93.3W   40 KT  45 MPH...INLAND
 72H  28/1800Z 36.5N  90.9W   30 KT  35 MPH...INLAND
 96H  29/1800Z 38.5N  80.5W   25 KT  30 MPH...INLAND
120H  30/1800Z 42.0N  66.5W   40 KT  45 MPH...POST-TROP/EXTRATROP


 

 

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7 minutes ago, olafminesaw said:

It's easy to get lost in the details with all kinds of data that's readily available. Better to take a step back and assess in 3-6 hour increments. We've seen steady improvement in structure throughout the day, but shear and  dry air has impeded progress. As shear begins to relax this evening, we should see the system begin to mix out the dry air, and begin fairly significant intensification by early tommorow morning. 

That is a valid and reasonable statement.  Wait until you see some consistency in the convective organization, and less of transient, sharp-edged very cold IR blow-ups.  I'd be more bullish on sooner RI if the entire system was not so elongated N S and that blob of discrete convection well S of the center didn't exist.

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The banter among the mets is really a fantastic way for novices like myself to increase understanding of tropical cyclone evolution. Please keep it up.

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The peak storm surge forecast does not appear too concerning for most areas in the cone. Is this due to landfall time coinciding with low tide? 
 

 

4605690D-F9B0-4EE3-9418-34DD73A82AC7.png

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1 minute ago, Hotair said:

The peak storm surge forecast does not appear too concerning for most areas in the cone. Is this due to landfall time coinciding with low tide? 
 

 

4605690D-F9B0-4EE3-9418-34DD73A82AC7.png

13 foot storm surge isn’t concerning to you?

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Just now, Nibor said:

13 foot storm surge isn’t concerning to you?

I was gonna say... I would sh*t my pants if i lived along the coast and was expecting a 13 foot storm surge. 

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5 minutes ago, Hotair said:

The peak storm surge forecast does not appear too concerning for most areas in the cone. Is this due to landfall time coinciding with low tide? 
 

 

4605690D-F9B0-4EE3-9418-34DD73A82AC7.png

Storm surge of 13 feet and it is forecast to extend up to 30 miles inland isnt concerning? 

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1 minute ago, jpeters3 said:

I was gonna say... I would sh*t my pants if i lived along the coast and was expecting a 13 foot storm surge. 

8 foot surge here from Sandy (10 ft storm tide because of the high tide) was pretty bad to say the least. Can’t imagine what a 13 ft surge would’ve been like. 

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7 minutes ago, Hotair said:

The peak storm surge forecast does not appear too concerning for most areas in the cone. Is this due to landfall time coinciding with low tide? 
 

 

4605690D-F9B0-4EE3-9418-34DD73A82AC7.png

You realize how far inland it will go in this region? For example, KLCH (Lake Charles Regional) is only 14.7ft above sea level, which is right next door to NWS LCH. This surge could have devastating impacts up to I-10 east of the center, including downtown Lake Charles because of the Calcasieu Ship Channel.

If Laura comes in at the upper-end of guidance, that WFO could likely be under water as both Rita & Ike surges came within less than 5 miles of them.

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30 minutes ago, jpeters3 said:

This logic is flawed.  You seem to state that you need good organization to get good organization.  But what you are failing to acknowledge is that there is a transitional time period between bad organization and good organization.

Not saying that RI is imminent or even that it will definitively happen, but just that it is irresponsible to throw in the towel based on ill-concieved notions.

I wasn't throwing in the towel and I was not being irresponsible.  Laura is a significant threat.  Just pointing caveats on its intensity potential.   And I did acknowledge there is a transition time by using the words "gradually" and "with time"

"You want to see a smooth ring of convection gradually develop, and cool with time, and wrap around the center,
and most importantly, persist for more than just a couple of hours."

NHC points out the caveats in terms of dry air and shear well in the 4pm CDT discussion.  They say dry air could still be a factor but don't go with it explicitly for now.  Shear will be a factor 6-12 hr before landfall, so it is prudent to not go too aggressive in the intensity at this point.  They did not change their intensity forecast at landfall from 10am CDT.
 

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Just now, vortex95 said:

I wasn't throwing in the towel and I was not being irresponsible.  Laura is a significant threat.  Just pointing caveats on its intensity potential.   And I did acknowledge there is a transition time by using the words "gradually" and "with time"

"You want to see a smooth ring of convection gradually develop, and cool with time, and wrap around the center,
and most importantly, persist for more than just a couple of hours."

NHC points out the caveats in terms of dry air and shear well in the 4pm CDT discussion.  They say dry air could still be a factor but don't go with it explicitly for now.  Shear will be a factor 6-12 hr before landfall, so it is prudent to not go too aggressive in the intensity at this point.  They did not change their intensity forecast at landfall from 10am CDT.
 

Got it.  Apologize for my critical post.

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3 minutes ago, MUWX said:

Storm surge of 13 feet and it is forecast to extend up to 30 miles inland isnt concerning? 

I apologize.  Thought this was showing a max of 9 ft.  My eyesight is not the greatest

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6 minutes ago, Hotair said:

I apologize.  Thought this was showing a max of 9 ft.  My eyesight is not the greatest

Yeah thankfully 9 feet in that area will be NBD.               /s

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Looking at latest visible satellite Laura seems to have pushed most of the dry out out of its core and a ring of convection is unzipping around the center. If this can hold may see more steady intensification start overnight 

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31 minutes ago, TPAwx said:

Yeah thankfully 9 feet in that area will be NBD.               /s

I’m sure 9ft would be problematic for those unfortunate enough to experience it,  but I would have expected higher surge from a possible CAT 3 on approach. 13 ft However does seem consistent with a major cane in the GOM 

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