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Major Hurricane Sam


Jtm12180
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This is a low res scan from the onboard radar from most recent recon pass west to east through Sam. The author seems uncertain about the maturity of the outer band, but this looks very much like degradation due to strong subsidence off the SW quad outer eyeband/wall. Also explains the semi-trichoidal motion. We're probably halfway through the current EWRC (at this given scan).



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From a “look perspective” it’s hard to imagine how a storm could be any stronger presentation wise about 5-8 hours ago. It definitely degraded since recons departed and even more so once recon arrived. A small tight core like Sam has it wouldn’t take much degradation for wind speed to come down quickly, unlike larger storms. There is literally zero hard evidence to support a cat 5 from earlier. However, sat estimates almost always fail to get the exact intensity and have a low bias for tiny storms, like Sam. It would honestly shock me if this didn’t peak at least 140 kts just from the ferocity of that satellite shot and the speed those eyewall towers were moving. Also, the pressure is consistent with a cat 5 storm of this size. That being said, there is zero hard evidence this made it to cat 5 and then does it really matter if it only maintained that intensity for a couple of hours? To us, yes, but NHC issues advisories based on intensity at time of advisory or based on hard evidence between them. Lacking the latter, this is going to stay a 4 in post analysis. Ida has a chance for an upgrade bc there was hard evidence, from wind measurements on land, recon, and pressure that it did reach the threshold. This to me was likely a stronger storm at peak but will be very unlikely to be upgraded without the hard evidence of nonstop recon and ground truth. 

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Sam seemed to struggle yesterday on the sw quadrant as well for awhile. Just remembering observing it yesterday for hours.
 

Beauty representation earlier. Looks good now, despite the skidding on the sw.  Based on pure hunch and eyeballing, it should kick out again and produce some acts of major+ characteristics next hours into tomorrow.

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1 hour ago, Amped said:

It's weakening faster than IDA after landfall.

You’re not lying! This looks like a major that just made landfall. Just even more impressive how resilient Ida was after landfall to maintain that intensity over land/marsh while watching this storm collapse over open ocean 

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Hurricane Sam Advisory Number  19
NWS National Hurricane Center Miami FL       AL182021
500 AM AST Mon Sep 27 2021

...SAM EXPECTED TO REMAIN A MAJOR HURRICANE FOR SEVERAL DAYS...
...HURRICANE HUNTER AIRCRAFT TO INVESTIGATE SAM LATER TODAY...


SUMMARY OF 500 AM AST...0900 UTC...INFORMATION
----------------------------------------------
LOCATION...15.2N 51.4W
ABOUT 800 MI...1290 KM ESE OF THE NORTHERN LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...130 MPH...215 KM/H
PRESENT MOVEMENT...NW OR 315 DEGREES AT 8 MPH...13 KM/H
MINIMUM CENTRAL PRESSURE...952 MB...28.12 INCHES


WATCHES AND WARNINGS
--------------------
There are no coastal watches or warnings in effect.


DISCUSSION AND OUTLOOK
----------------------
At 500 AM AST (0900 UTC), the center of Hurricane Sam was located 
near latitude 15.2 North, longitude 51.4 West.  Sam is moving toward 
the northwest near 8 mph (13 km/h).  This general motion is expected 
to continue for the next several days, with an increase in forward 
speed beginning on Thursday.

Maximum sustained winds are near 130 mph (215 km/h) with higher 
gusts.  Sam is a category 4 hurricane on the Saffir-Simpson 
Hurricane Wind Scale.  Little change in strength is expected during 
the next day or so.  Thereafter, some slow weakening is forecast 
through midweek, although Sam should remain a major hurricane.

Sam is a small hurricane.  Hurricane-force winds extend outward up 
to 30 miles (45 km) from the center and tropical-storm-force winds 
extend outward up to 105 miles (165 km).

The estimated minimum central pressure is 952 mb (28.12 inches).


HAZARDS AFFECTING LAND
----------------------
SURF:  Swells generated by Sam will reach the Lesser Antilles today
and impact these islands for the next several days.  These swells
could cause life-threatening surf and rip current conditions. Please
consult products from your local weather office.


NEXT ADVISORY
-------------
Next complete advisory at 1100 AM AST.

$$
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Hurricane Sam Discussion Number  19
NWS National Hurricane Center Miami FL       AL182021
500 AM AST Mon Sep 27 2021

The satellite presentation of Sam deteriorated overnight, as GOES-16 
infrared imagery showed periodic disruptions to Sam's inner core 
convection. The eye has not been readily apparent in conventional 
satellite imagery for much of the night, although very recent 
imagery suggests an eye could be re-emerging. Data from the 
reconnaissance aircraft last night indicated that an eyewall 
replacement cycle (ERC) was underway, and some dry mid-level air 
impinging on the western side of the circulation could also be 
negatively impacting Sam. No recent high-resolution microwave data 
is available, but an earlier scatterometer pass revealed that the 
tropical-storm-force wind radii had expanded just a bit in the 
eastern semicircle of the hurricane. The initial intensity is 
lowered to 115 kt for this advisory based on a blend of the 
objective and subjective Dvorak current intensity estimates. A NOAA 
hurricane hunter aircraft is scheduled to investigate Sam later this 
morning, which will provide crucial data to assess changes in Sam's 
structure and intensity.

The initial motion is estimated to be northwestward, or 315/7 kt. A 
subtropical ridge to the north and northeast of Sam will remain the 
primary steering mechanism over the next several days, and Sam is 
expected to maintain a northwestward heading through midweek. Then, 
a mid- to upper-level trough is forecast to dig southward over the 
western Atlantic late this week. The deep-layer southerly flow ahead 
of this feature should cause Sam to move faster toward the 
north-northwest by 96 h, followed by a northward acceleration 
thereafter. The NHC forecast track is shifted slightly to the right 
of the previous one through the first 48-60 h of the forecast 
period, which accounts for the more northwestward initial motion 
observed during the past 12 h. Otherwise, the NHC track is virtually 
unchanged as the guidance has remained fairly consistent.  

Sam's intensity has likely peaked now that an ERC has commenced, but 
environmental conditions should allow Sam to persist as a major 
hurricane for the next several days. Sea-surface temperatures are 
expected to be 28 deg C or greater along Sam's track through 120 h, 
and the vertical wind shear is forecast to remain weak (< 10 kt) 
through at least midweek. Thus, the official NHC intensity forecast 
only shows very gradual weakening during the next several days, 
generally following the HCCA and IVCN consensus aids. Given the 
lower initial intensity of Sam, the latest NHC forecast is once 
again lower than the previous one. By 120 h, southerly shear 
associated with the deep-layer trough is forecast to increase over 
Sam, which should induce more weakening by this weekend. 


FORECAST POSITIONS AND MAX WINDS

INIT  27/0900Z 15.2N  51.4W  115 KT 130 MPH
 12H  27/1800Z 15.9N  52.2W  115 KT 130 MPH
 24H  28/0600Z 16.8N  53.3W  115 KT 130 MPH
 36H  28/1800Z 17.7N  54.4W  115 KT 130 MPH
 48H  29/0600Z 18.6N  55.6W  110 KT 125 MPH
 60H  29/1800Z 19.6N  57.1W  110 KT 125 MPH
 72H  30/0600Z 21.0N  58.8W  110 KT 125 MPH
 96H  01/0600Z 24.9N  61.6W  110 KT 125 MPH
120H  02/0600Z 30.5N  62.0W  105 KT 120 MPH

$$
Forecaster Reinhart
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As impressive as the rapid intensification was, the period of weakening has been fascinating as well. It looks like the ERC, which reorganizes a hurricane's inner core, provided the opening for relatively light shear to impart dry air into the more vulnerable core, causing significant disruption. 

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