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Major Hurricane Sam


Jtm12180
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3 hours ago, Windspeed said:

OTS is not in stone and too far out. You still have a potential maritime block over New Foundland with a cutoff trough over the ECONUS. Can't rule out phase interaction with trough until we're in the midrange. Writing off to OTS at 220-240 hrs is... premature.

At least allow interaction time to move into the midrange to provide better timing and positional placement of features.



 

Gfs is coming in further south so far.

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Still pretty far out there though in terms of time. As I usually do with MDR systems, I’m not really fully on board until I see it at Antilles. That’ll be a key point as we’ll know whether it’s taking the first potential escape route into the ridge weakness or not.

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2 minutes ago, CheeselandSkies said:

I'm surprised it's beating the "south=weaker" drum, since the more southerly track will put 18/Sam through the warmest possible water in front of it.

Euro is notoriously bad with modeling TC intensity so not much to say in this regard. Lower resolution ensembles don't help in this regard.

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BULLETIN
Tropical Storm Sam Advisory Number   4
NWS National Hurricane Center Miami FL       AL182021
1100 AM AST Thu Sep 23 2021

...DEPRESSION STRENGTHENS INTO TROPICAL STORM SAM, THE 18TH NAMED
STORM OF THE SEASON...
...NOW FORECAST TO BECOME A HURRICANE TOMORROW...


SUMMARY OF 1100 AM AST...1500 UTC...INFORMATION
-----------------------------------------------
LOCATION...10.9N 38.1W
ABOUT 1745 MI...2805 KM ESE OF THE NORTHERN LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...50 MPH...85 KM/H
PRESENT MOVEMENT...W OR 280 DEGREES AT 16 MPH...26 KM/H
MINIMUM CENTRAL PRESSURE...1003 MB...29.62 INCHES


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


DISCUSSION AND OUTLOOK
----------------------
At 1100 AM AST (1500 UTC), the center of Tropical Storm Sam was
located near latitude 10.9 North, longitude 38.1 West. Sam is moving
toward the west near 16 mph (26 km/h) and this general motion is
expected to continue over the next several days, but with a gradual
slowdown in forward motion.

Recent sallite wind data indicates maximum sustained winds have
increased to near 50 mph (85 km/h) with higher gusts. Additional
strengthening is forecast over the next several days, and Sam is now
forecast to become a hurricane tomorrow and be near major hurricane
intensity by the end of the weekend.

Tropical-storm-force winds extend outward up to 45 miles (75 km)
from the center.

The estimated minimum central pressure is 1003 mb (29.62 inches).
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Tropical Storm Sam Discussion Number   4
NWS National Hurricane Center Miami FL       AL182021
1100 AM AST Thu Sep 23 2021

Overnight and this morning, the satellite structure of the tropical
cyclone has been improving, with prominent curved bands, and obvious
low-level cloud motions that indicate the circulation is becoming
established within the convection. In particular, an SSMIS microwave
pass at 0653 UTC indicated a substantial improvement in the
convective structure, with a well-defined curved band wrapping
three-quarters of the way around the center in both the 91- and
37-GHz channels. ASCAT-B wind retrievals at 1234 UTC also indicated
a tight, well-defined circulation had formed, with peak winds of
44-kt on the north side of the vortex. Subjective Dvorak satellite
intensity estimates are now T3.5/55-kt from SAB and T2.5/35-kt from
TAFB. In addition, the latest objective intensity estimates from
UW-CIMSS ADT and SATCON were at 35-kt and 43-kt respectively. Given
the recent scatterometer data, the intensity has been set to 45-kt
for this advisory. Thus, Tropical Depression 18 has been upgraded to
Tropical Storm Sam. It is noteworthy that this is the 2nd earliest
formation of the 18th named storm in the Atlantic basin, moving
ahead of the 2005 hurricane season, and only trailing last year.

Sam continues to move to the west-northwest with an estimated motion
at 280/14 kt.  A prominent mid-level ridge remains entrenched to the
north of the cyclone, and this feature should continue to steer Sam
to the west-northwest over the next 2-3 days. Over this period, the
ridge orientation actually shifts more westward ahead of the cyclone
as a deep-layer trough digs in well northeast of Sam. This gradual
change in the synoptic pattern should also result in a slowdown in
Sam's forward motion over the next 72 hours. While the track
guidance remains in good agreement over this period, larger spread
begins to take shape beyond the day 3 forecast. Similar to
yesterday, the ECMWF model and its ensemble mean flanks the
southwest side of the guidance envelop, while the GFS is on the
northeast side by day 5. These differences appear to be partially
related to the mid-level ridge intensity on the western end, which
could begin to be eroded by a mid-latitude trough off the eastern
United States in 120-h. In addition, differences in both the size
and intensity of Sam may also play a role in its ultimate track
evolution. For this advisory, the latest NHC track forecast remains
close to the consensus aids TCVN and TCVE, which represents a slight
shift westward and a bit faster motion compared to the previous
forecast. Because Sam is forecast to slow down, it remains too early
to determine what impacts, direct or indirect, could be felt by the
Lesser Antilles by this cyclone.

The previously mentioned SSMIS microwave imagery also indicated that
the low-level center has become better aligned with the mid-level
vortex, perhaps a bit earlier than anticipated given the
scatterometer data from last night. This improvement in structure,
combined with favorable low vertical wind shear under 10 kt and warm
28-29 C sea-surface temperatures, argues for significant
intensification. In fact, the GFS-SHIPS rapid intensification index
now give Sam a 39 percent chance of a 65-kt increase over the next
72 hours, which is more than 7 times the climatological value. Thus,
the NHC intensity forecast has been raised quite a bit from the
prior one, especially in the short-term. The latest forecast now
makes Sam a hurricane in 36 hours, and a major hurricane in 72
hours. This intensity forecast is just a shade under the latest HCCA
consensus aid. Thereafter, a more gradual intensification rate is
forecast. By this period it is possible that Sam could undergo hard
to predict inner-core changes such as eyewall replacement cycles. In
addition, the ECMWF-SHIPS suggests that the shear may also increase
a little in days 4-5 which also argues for a bit slower rate of
intensification for this period.


FORECAST POSITIONS AND MAX WINDS

INIT  23/1500Z 10.9N  38.1W   45 KT  50 MPH
 12H  24/0000Z 11.3N  40.3W   50 KT  60 MPH
 24H  24/1200Z 11.9N  42.9W   60 KT  70 MPH
 36H  25/0000Z 12.3N  45.0W   70 KT  80 MPH
 48H  25/1200Z 12.7N  46.7W   80 KT  90 MPH
 60H  26/0000Z 13.2N  48.2W   90 KT 105 MPH
 72H  26/1200Z 13.7N  49.4W  100 KT 115 MPH
 96H  27/1200Z 15.3N  52.1W  105 KT 120 MPH
120H  28/1200Z 17.4N  55.2W  110 KT 125 MPH

$$
Forecaster Papin
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14 minutes ago, Windspeed said:

We have Sam. Let the Dr. Seuss'ing begin.
c701986b9b11a7a61008dd9214ffd9b6.jpg

This year's list has been good for memes/pop culture references, especially recently.

You had Peter (Griffin)/Peter Rose

Peter & Rose dissipating (Petered out/Rose..bud)

There's also a locomotive in The Railway Series/Thomas the Tank Engine & Friends named "Peter Sam."

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13 minutes ago, OSUmetstud said:

These are the historic tracks in September/October within 200 NM of the NHC day 5 forecast point. Most recurve out to sea, a few makes to the US southeast, a few to the US northeast, and a few to Atlantic Canada. 

Sam Historic.PNG

Why would your starting point be a day 5 projection subject to forecast error instead of where the storm is now? Oh wait, because that’s less fun and has a way higher percentage of OTS.

unamed 1893 would be alright tho…looks like the only realistic post 9/20.  I personally would like to see inez 2. That would be an insanely fun storm to track.

 

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10 minutes ago, Tezeta said:

Why would your starting point be a day 5 projection subject to forecast error instead of where the storm is now? Oh wait, because that’s less fun and has a way higher percentage of OTS.

unamed 1893 would be alright tho…looks like the only realistic post 9/20.  I personally would like to see inez 2. That would be an insanely fun storm to track.

 

lol I didn't even look at that. I was just curious where from Day 5 onward it would look like. The average track error at Day 5 is 172 NM so it's not completely without basis. I mean you could run all storms from the current point and see what it looks like if you want. 

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Just now, OSUmetstud said:

lol I didn't even look at that. I was just curious where from Day 5 onward it would look like. The average track error at Day 5 is 172 NM so it's not completely without basis. I mean you could run all storms from the current point and see what it looks like if you want. 

I took a look, which is why I think Inez would be what I am rooting for

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  • Jtm12180 changed the title to Major Hurricane Sam

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