Major Hurricane Sam

[Amped]

A few years back Dorian had a ~137kt SFMR with about the same pressure and NHC didn't upgrade it to a CAT5 since FL winds weren't high enough.   Wonder if they do the same here?

Also there  no rain flagged SFMR obs in the core.  That's pretty unusual.

[WxWatcher007]

3 minutes ago, Amped said:

A few years back Dorian had a ~137kt SFMR with about the same pressure and NHC didn't upgrade it to a CAT5 since FL winds weren't high enough.   Wonder if they do the same here?

Probably? Over the last few years there has been an apparent high bias with SFMR in very intense hurricanes. 

https://twitter.com/AndrewHagen/status/1441893019435872267?s=20

[Wannabehippie]

945mb on first pass.

[WxWatcher007]

Latest VDM

 

Product: NOAA Vortex Message (URNT12 KWBC)
Transmitted: 25th day of the month at 23:21Z
Agency: National Oceanic and Atmospheric Administration (NOAA)
Aircraft: Lockheed WP-3D Orion (Reg. Num. N42RF)
Storm Name: Sam
Storm Number & Year: 18 in 2021 (flight in the North Atlantic basin)
Mission: Second flight of a sequence of non-tasked research missions into this system
Observation Number: 17 ( See all messages of this type for this mission. )

A. Time of Center Fix: 25th day of the month at 22:59:16Z
B. Center Fix Coordinates: 13.34N 48.64W
B. Center Fix Location: 738 statute miles (1,188 km) to the E (89°) from Bridgetown, Barbados.
C. Minimum Height at Standard Level: 2,638m (8,655ft) at 700mb
D. Minimum Sea Level Pressure: 946mb (27.94 inHg)
E. Dropsonde Surface Wind at Center: From 200° at 16kts (From the SSW at 18mph)
F. Eye Character: Closed
G. Eye Shape & Diameter: Circular with a diameter of 13 nautical miles (15 statute miles)
H. Estimated (by SFMR or visually) Maximum Surface Wind Inbound: 136kts (156.5mph)
I. Location & Time of the Estimated Maximum Surface Wind Inbound: 6 nautical miles to the NNE (31°) of center fix at 22:57:47Z
J. Maximum Flight Level Wind Inbound: From 123° at 139kts (From the ESE at 160.0mph)
K. Location & Time of the Maximum Flight Level Wind Inbound: 8 nautical miles to the NNE (31°) of center fix at 22:57:16Z
L. Estimated (by SFMR or visually) Maximum Surface Wind Outbound: 103kts (118.5mph)
M. Location & Time of the Estimated Maximum Surface Wind Outbound: 6 nautical miles to the SSW/SW (214°) of center fix at 23:00:53Z
N. Maximum Flight Level Wind Outbound: From 287° at 103kts (From the WNW at 118.5mph)
O. Location & Time of the Maximum Flight Level Wind Outbound: 6 nautical miles to the SSW/SW (214°) of center fix at 23:00:46Z
P. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 10°C (50°F) at a pressure alt. of 3,068m (10,066ft)
Q. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 20°C (68°F) at a pressure alt. of 3,057m (10,030ft)
R. Dewpoint Temp (collected at same location as temp inside eye): 6°C (43°F)
R. Sea Surface Temp (collected at same location as temp inside eye): Not Available
S. Fix Determined By: Penetration, Radar, Pressure and Temperature
S. Fix Level: 700mb
T. Navigational Fix Accuracy: 0.01 nautical miles
T. Meteorological Accuracy: 1 nautical mile

Remarks Section:
 

Maximum Flight Level Wind: 139kts (~ 160.0mph) which was observed 8 nautical miles to the NNE (31°) from the flight level center at 22:57:16Z

[WxWatcher007]

Don't see the FL winds to support it in this set of data, but there's an unflagged 141kt SFMR on this latest pass (SE to NW). 

[WxWatcher007]

...and in the next set of data we see FL winds of 130, 132kts and another SFMR of 144kts. Could be a gust and biased high, but clearly a high end Atlantic hurricane. Quite impressive. 

[Windspeed]

Don't see the FL winds to support it in this set of data, but there's an unflagged 141kt SFMR on this latest pass (SE to NW). 

I'm a little leary of >140 kt SFMR readings without similiar flight level readings as well. But Sam is no doubt an intense hurricane. Especially in this region of the MDR. It's in rare company. Think Hugo and Irma. I'd be comfortable with 135 kts / 155 mph on the next advisory.

[WxWatcher007]

1 minute ago, Windspeed said:

11 minutes ago, WxWatcher007 said:

Don't see the FL winds to support it in this set of data, but there's an unflagged 141kt SFMR on this latest pass (SE to NW). 

I'm a little leary of >140 kt SFMR readings without similiar flight level readings as well. But Sam is no doubt an intense hurricane. Especially in this region of the MDR. It's in rare company. Think Hugo and Irma. I'd be comfortable with 135 kts / 155 mph on the next advisory.

Agree. 

Also, here's a great dropsonde for posterity. It went for one hell of a ride  

 

Product: NOAA Temp Drop (Dropsonde) Message (UZNT13 KWBC)
Transmitted: 26th day of the month at 0:12Z
Agency: National Oceanic and Atmospheric Administration (NOAA)
Aircraft: Lockheed WP-3D Orion (Reg. Num. N42RF)
Storm Name: Sam
Storm Number: 18 (flight in the North Atlantic basin)
Mission: Second flight of a sequence of non-tasked research missions into this system
Observation Number: 27 ( See all messages of this type for this mission. )

Part A...
 

Date: Near the closest hour of 0Z on the 26th day of the month
Highest Mandatory Level For Which Wind Was Reported: 700mb
Coordinates: 13.3N 48.7W
Location: 734 statute miles (1,181 km) to the E (89°) from Bridgetown, Barbados.
Marsden Square: 041 ( About )
 

Surface and Standard Isobaric Surfaces
Level	Geo. Height	Air Temp.	Dew Point	Wind Direction	Wind Speed
1000mb	-400m (-1,312 ft)	This level does not exist in this area of the storm above the surface level.
956mb (28.23 inHg)	Surface (Sea Level)	24.0°C (75.2°F)	23.3°C (74°F)	110° (from the ESE)	162 knots (186 mph)
925mb	285m (935 ft)	22.2°C (72.0°F)	22.1°C (72°F)	125° (from the SE)	174 knots (200 mph)
850mb	1,022m (3,353 ft)	20.2°C (68.4°F)	20.0°C (68°F)	165° (from the SSE)	115 knots (132 mph)
700mb	2,687m (8,816 ft)	14.0°C (57.2°F)	12.8°C (55°F)	220° (from the SW)	96 knots (110 mph)

Information About Radiosonde:
- Launch Time: 23:56Z
- About Sonde: A descending radiosonde tracked automatically by satellite navigation with no solar or infrared correction.

Remarks Section...
 

Dropsonde Location: Dropped in eyewall 135° (SE) from the eye center.

Highest altitude where wind was reported:
- Location: 13.35N 48.70W
- Time: 23:56:15Z

Lowest altitude where wind was reported:
- Location: 13.49N 48.73W
- Time: 0:00:53Z

Mean Boundary Level Wind (mean wind in the lowest 500 geopotential meters of the sounding):
- Wind Direction: 130° (from the SE)
- Wind Speed: 158 knots (182 mph)

Deep Layer Mean Wind (average wind over the depth of the sounding):
- Wind Direction: 165° (from the SSE)
- Wind Speed: 105 knots (121 mph)
- Depth of Sounding: From 699mb to 955mb

Average Wind Over Lowest Available 150 geopotential meters (gpm) of the sounding:
- Lowest 150m: 157 gpm - 7 gpm (515 geo. feet - 23 geo. feet)
- Wind Direction: 115° (from the ESE)
- Wind Speed: 161 knots (185 mph)

Sounding Software Version: AEV 30406
 

Part B: Data for Significant Levels...
 

Significant Temperature And Relative Humidity Levels
Level	Air Temperature	Dew Point
956mb (Surface)	24.0°C (75.2°F)	23.3°C (74°F)
850mb	20.2°C (68.4°F)	20.0°C (68°F)
719mb	14.4°C (57.9°F)	14.2°C (58°F)
692mb	14.6°C (58.3°F)	12.1°C (54°F)

 

Significant Wind Levels
Level	Wind Direction	Wind Speed
956mb (Surface)	110° (from the ESE)	162 knots (186 mph)
954mb	110° (from the ESE)	161 knots (185 mph)
953mb	110° (from the ESE)	167 knots (192 mph)
951mb	115° (from the ESE)	168 knots (193 mph)
936mb	125° (from the SE)	147 knots (169 mph)
925mb	125° (from the SE)	174 knots (200 mph)
921mb	130° (from the SE)	169 knots (194 mph)
916mb	140° (from the SE)	171 knots (197 mph)
910mb	140° (from the SE)	162 knots (186 mph)
905mb	140° (from the SE)	144 knots (166 mph)
903mb	140° (from the SE)	139 knots (160 mph)
894mb	145° (from the SE)	144 knots (166 mph)
889mb	155° (from the SSE)	132 knots (152 mph)
879mb	160° (from the SSE)	122 knots (140 mph)
871mb	155° (from the SSE)	124 knots (143 mph)
866mb	155° (from the SSE)	113 knots (130 mph)
862mb	160° (from the SSE)	121 knots (139 mph)
856mb	160° (from the SSE)	113 knots (130 mph)
850mb	165° (from the SSE)	115 knots (132 mph)
699mb	220° (from the SW)	96 knots (110 mph)

[WxWatcher007]

Here's the visual. Again, for posterity  

[Windspeed]

lol at that 921 mb wind. I suppose if the pressure falls any further or the wind / pressure gradiant had a little more time before any structural degradation of the eyewall, it might pull off Cat 5.

Sam is a compact hurricane. I suppose we'll just have to see how long the core can maintain this structure without concentric banding getting the upper hand. Irma was pretty resilient to full cycle ERCs in this region back in 2017. It would pull off some some kind of absorption of the outer band before it could fully become concentric.

[Ed, snow and hurricane fan]

13 minutes ago, WxWatcher007 said:

Agree. 

Also, here's a great dropsonde for posterity. It went for one hell of a ride  

 

Product: NOAA Temp Drop (Dropsonde) Message (UZNT13 KWBC)
Transmitted: 26th day of the month at 0:12Z
Agency: National Oceanic and Atmospheric Administration (NOAA)
Aircraft: Lockheed WP-3D Orion (Reg. Num. N42RF)
Storm Name: Sam
Storm Number: 18 (flight in the North Atlantic basin)
Mission: Second flight of a sequence of non-tasked research missions into this system
Observation Number: 27 ( See all messages of this type for this mission. )

Part A...
 

Date: Near the closest hour of 0Z on the 26th day of the month
Highest Mandatory Level For Which Wind Was Reported: 700mb
Coordinates: 13.3N 48.7W
Location: 734 statute miles (1,181 km) to the E (89°) from Bridgetown, Barbados.
Marsden Square: 041 ( About )
 

Surface and Standard Isobaric Surfaces
Level	Geo. Height	Air Temp.	Dew Point	Wind Direction	Wind Speed
1000mb	-400m (-1,312 ft)	This level does not exist in this area of the storm above the surface level.
956mb (28.23 inHg)	Surface (Sea Level)	24.0°C (75.2°F)	23.3°C (74°F)	110° (from the ESE)	162 knots (186 mph)
925mb	285m (935 ft)	22.2°C (72.0°F)	22.1°C (72°F)	125° (from the SE)	174 knots (200 mph)
850mb	1,022m (3,353 ft)	20.2°C (68.4°F)	20.0°C (68°F)	165° (from the SSE)	115 knots (132 mph)
700mb	2,687m (8,816 ft)	14.0°C (57.2°F)	12.8°C (55°F)	220° (from the SW)	96 knots (110 mph)

Information About Radiosonde:
- Launch Time: 23:56Z
- About Sonde: A descending radiosonde tracked automatically by satellite navigation with no solar or infrared correction.

Remarks Section...
 

Dropsonde Location: Dropped in eyewall 135° (SE) from the eye center.

Highest altitude where wind was reported:
- Location: 13.35N 48.70W
- Time: 23:56:15Z

Lowest altitude where wind was reported:
- Location: 13.49N 48.73W
- Time: 0:00:53Z

Mean Boundary Level Wind (mean wind in the lowest 500 geopotential meters of the sounding):
- Wind Direction: 130° (from the SE)
- Wind Speed: 158 knots (182 mph)

Deep Layer Mean Wind (average wind over the depth of the sounding):
- Wind Direction: 165° (from the SSE)
- Wind Speed: 105 knots (121 mph)
- Depth of Sounding: From 699mb to 955mb

Average Wind Over Lowest Available 150 geopotential meters (gpm) of the sounding:
- Lowest 150m: 157 gpm - 7 gpm (515 geo. feet - 23 geo. feet)
- Wind Direction: 115° (from the ESE)
- Wind Speed: 161 knots (185 mph)

Sounding Software Version: AEV 30406
 

Part B: Data for Significant Levels...
 

Significant Temperature And Relative Humidity Levels
Level	Air Temperature	Dew Point
956mb (Surface)	24.0°C (75.2°F)	23.3°C (74°F)
850mb	20.2°C (68.4°F)	20.0°C (68°F)
719mb	14.4°C (57.9°F)	14.2°C (58°F)
692mb	14.6°C (58.3°F)	12.1°C (54°F)

 

Significant Wind Levels
Level	Wind Direction	Wind Speed
956mb (Surface)	110° (from the ESE)	162 knots (186 mph)
954mb	110° (from the ESE)	161 knots (185 mph)
953mb	110° (from the ESE)	167 knots (192 mph)
951mb	115° (from the ESE)	168 knots (193 mph)
936mb	125° (from the SE)	147 knots (169 mph)
925mb	125° (from the SE)	174 knots (200 mph)
921mb	130° (from the SE)	169 knots (194 mph)
916mb	140° (from the SE)	171 knots (197 mph)
910mb	140° (from the SE)	162 knots (186 mph)
905mb	140° (from the SE)	144 knots (166 mph)
903mb	140° (from the SE)	139 knots (160 mph)
894mb	145° (from the SE)	144 knots (166 mph)
889mb	155° (from the SSE)	132 knots (152 mph)
879mb	160° (from the SSE)	122 knots (140 mph)
871mb	155° (from the SSE)	124 knots (143 mph)
866mb	155° (from the SSE)	113 knots (130 mph)
862mb	160° (from the SSE)	121 knots (139 mph)
856mb	160° (from the SSE)	113 knots (130 mph)
850mb	165° (from the SSE)	115 knots (132 mph)
699mb	220° (from the SW)	96 knots (110 mph)

Cool seeing how sonde is rotating around the eye as wind directions shift almost 90 degrees.

[WxWatcher007]

9 minutes ago, Ed, snow and hurricane fan said:

Cool seeing how sonde is rotating around the eye as wind directions shift almost 90 degrees.

It's awesome, and there are multiple dropsondes doing it. This has been a really cool recon flight to watch. 

[WxWatcher007]

Both recon flights have ended, so now we wait to see what the NHC does at 11. 

[Windspeed]

Both recon flights have ended, so now we wait to see what the NHC does at 11. 

Yeah, and just as you would have it, as reconnaissance leaves, a strong CB encircles the eyewall. That's the way it goes. lol...

[thunderbolt]

1 minute ago, Windspeed said:

Yeah, and just as you would have it, as reconnaissance leaves, a strong CB encircles the eyewall. That's the way it goes. lol...

Just by looking at the animation if I were to guess A hi end cat 4 possibly cat  5

[WxWatcher007]

Really interesting discussion 

Hurricane Sam Discussion Number  14
NWS National Hurricane Center Miami FL       AL182021
1100 PM AST Sat Sep 25 2021

It's been an interesting evening with regards to analyzing the 
various data from a NOAA Hurricane Hunter research flight into 
Hurricane Sam. Dropsonde data in both the southeast and northwest 
quadrants indicate that small eyewall mesovortices and possibly even 
tornado-scale vortices were present based on the wind profiles 
showing sharply opposite-direction winds from what would normally be 
expected in those regions of the hurricane. Some dropsonde surface 
winds have been as high as 162 kt, which is more representative of a 
gust, while SFMR surface winds have been as high as 133 kt. However, 
the strongest 700-mb flight-level winds have been 138-139 kt in the 
northeastern quadrant, which equates to about 125-kt tangential 
surface winds. Three dropsondes released in the eye indicate that 
the pressure had remained steady at 943-944 mb during the duration 
of the aircraft reconnoiter. That pressure equates to about 125 kt 
based on various pressure-wind relationships. Based on that estimate 
and the 700-mb flight-level to surface-wind conversion, the advisory 
intensity is 125 kt, which is representative of the mean tangential 
winds and no localized wind perturbations.

The initial motion is toward the west-northwest, or 295/07 kt.  
Not to sound like a broken record, but no significant changes were 
made to the previous track forecast and reasoning. Sam is expected 
to move slowly west-northwestward and northwestward over the next 
few days around the southwestern periphery of a deep-layer 
subtropical ridge that is situated to the north and northeast of the 
small hurricane. On days 4 and 5, an upper-level trough/low is 
forecast to dig southward and amplify off the U.S. east coast and 
extend all the way to the Bahamas. This feature should act to lift 
Sam northward at a faster forward speed. The latest NHC model 
guidance based on 12Z and 18Z model runs has shifted noticeably to 
the east of the previous runs, and the new NHC track forecast has 
been nudged in that direction as well. However, since the NOAA G-IV 
jet aircraft has been out there sampling the environment around 
Sam, it's best to remain conservative and not shift the track any 
farther to the east until the new 00Z model runs with that new 
aircraft data come in for the next advisory package at 0600Z. The 
new NHC track forecast lies about halfway between the previous 
advisory track on the left and the tightly packed consensus track 
models on the right.

The radar images from the reconnaissance aircraft indicated that the 
eyewall was thin in many locations due to dry-air intrusions, and 
the latest SHIPS intensity output indicates that Sam will remain 
within a fairly dry mid-level environment. Also, the depth of the 
warm water beneath the hurricane isn't overly deep, which could 
result in cold upwelling owing to Sam's slow forward motion of only 
5-7 kt during the next couple of days. Eyewall replacement cycles 
are also likely now due to the hurricane's small size and strong 
intensity. Thus, fluctuations in intensity seem likely for the next 
couple of days even though the vertical wind shear is expected to 
remain quite low at only 5-10 kt. On days 3-5, however, the shear is 
forecast to increase to 15-20 kt from the southwest, which is 
expected to induce a slow weakening trend. However, it is likely 
that Sam will remain a major hurricane through 120 h, even on days 
3-5 due to the cyclone moving over warmer and deeper water during 
that 3-day period. The new official intensity forecast is 
essentially the same as the previous advisory, and remains above the 
consensus model and is near the higher end of the intensity 
guidance.

FORECAST POSITIONS AND MAX WINDS

INIT  26/0300Z 13.5N  49.0W  125 KT 145 MPH
 12H  26/1200Z 14.0N  49.9W  130 KT 150 MPH
 24H  27/0000Z 14.7N  51.0W  125 KT 145 MPH
 36H  27/1200Z 15.4N  52.1W  120 KT 140 MPH
 48H  28/0000Z 16.3N  53.2W  120 KT 140 MPH
 60H  28/1200Z 17.1N  54.3W  115 KT 130 MPH
 72H  29/0000Z 18.0N  55.6W  115 KT 130 MPH
 96H  30/0000Z 20.1N  58.5W  110 KT 125 MPH
120H  01/0000Z 23.7N  61.4W  110 KT 125 MPH

$$
Forecaster Stewart

 

[Windspeed]

Really interesting discussion 

Hurricane Sam Discussion Number  14NWS National Hurricane Center Miami FL       AL1820211100 PM AST Sat Sep 25 2021It's been an interesting evening with regards to analyzing the various data from a NOAA Hurricane Hunter research flight into Hurricane Sam. Dropsonde data in both the southeast and northwest quadrants indicate that small eyewall mesovortices and possibly even tornado-scale vortices were present based on the wind profiles showing sharply opposite-direction winds from what would normally be expected in those regions of the hurricane. Some dropsonde surface winds have been as high as 162 kt, which is more representative of a gust, while SFMR surface winds have been as high as 133 kt. However, the strongest 700-mb flight-level winds have been 138-139 kt in the northeastern quadrant, which equates to about 125-kt tangential surface winds. Three dropsondes released in the eye indicate that the pressure had remained steady at 943-944 mb during the duration of the aircraft reconnoiter. That pressure equates to about 125 kt based on various pressure-wind relationships. Based on that estimate and the 700-mb flight-level to surface-wind conversion, the advisory intensity is 125 kt, which is representative of the mean tangential winds and no localized wind perturbations.The initial motion is toward the west-northwest, or 295/07 kt.  Not to sound like a broken record, but no significant changes were made to the previous track forecast and reasoning. Sam is expected to move slowly west-northwestward and northwestward over the next few days around the southwestern periphery of a deep-layer subtropical ridge that is situated to the north and northeast of the small hurricane. On days 4 and 5, an upper-level trough/low is forecast to dig southward and amplify off the U.S. east coast and extend all the way to the Bahamas. This feature should act to lift Sam northward at a faster forward speed. The latest NHC model guidance based on 12Z and 18Z model runs has shifted noticeably to the east of the previous runs, and the new NHC track forecast has been nudged in that direction as well. However, since the NOAA G-IV jet aircraft has been out there sampling the environment around Sam, it's best to remain conservative and not shift the track any farther to the east until the new 00Z model runs with that new aircraft data come in for the next advisory package at 0600Z. The new NHC track forecast lies about halfway between the previous advisory track on the left and the tightly packed consensus track models on the right.The radar images from the reconnaissance aircraft indicated that the eyewall was thin in many locations due to dry-air intrusions, and the latest SHIPS intensity output indicates that Sam will remain within a fairly dry mid-level environment. Also, the depth of the warm water beneath the hurricane isn't overly deep, which could result in cold upwelling owing to Sam's slow forward motion of only 5-7 kt during the next couple of days. Eyewall replacement cycles are also likely now due to the hurricane's small size and strong intensity. Thus, fluctuations in intensity seem likely for the next couple of days even though the vertical wind shear is expected to remain quite low at only 5-10 kt. On days 3-5, however, the shear is forecast to increase to 15-20 kt from the southwest, which is expected to induce a slow weakening trend. However, it is likely that Sam will remain a major hurricane through 120 h, even on days 3-5 due to the cyclone moving over warmer and deeper water during that 3-day period. The new official intensity forecast is essentially the same as the previous advisory, and remains above the consensus model and is near the higher end of the intensity guidance.FORECAST POSITIONS AND MAX WINDSINIT  26/0300Z 13.5N  49.0W  125 KT 145 MPH12H  26/1200Z 14.0N  49.9W  130 KT 150 MPH24H  27/0000Z 14.7N  51.0W  125 KT 145 MPH36H  27/1200Z 15.4N  52.1W  120 KT 140 MPH48H  28/0000Z 16.3N  53.2W  120 KT 140 MPH60H  28/1200Z 17.1N  54.3W  115 KT 130 MPH72H  29/0000Z 18.0N  55.6W  115 KT 130 MPH96H  30/0000Z 20.1N  58.5W  110 KT 125 MPH120H  01/0000Z 23.7N  61.4W  110 KT 125 MPH$$Forecaster Stewart

 

Yeah I get the suspect meso/microvortices directtional changes and the 700mb 10% reduction but there was plenty of redundant data to support 130-135 kts / 155 mph on the advisory package. Either way, still an impressively intense Category 4 Cape Verde hurricane.

[Maestrobjwa]

2 hours ago, Windspeed said:

Yeah, and just as you would have it, as reconnaissance leaves, a strong CB encircles the eyewall. That's the way it goes. lol...

"Wait wait--turn those planes around!"

[Amped]

Quote

Based on that estimate and the 700-mb flight-level to surface-wind conversion, the advisory intensity is 125 kt, which is representative of the mean tangential winds and no localized wind perturbations.

Here's how you know this is a fish storm.   You don't see this quote in an nhc discussion when a storm is near land and warnings are up.

[ncforecaster89]

6 hours ago, Windspeed said:

6 hours ago, WxWatcher007 said:

Really interesting discussion 

Hurricane Sam Discussion Number  14NWS National Hurricane Center Miami FL       AL1820211100 PM AST Sat Sep 25 2021It's been an interesting evening with regards to analyzing the various data from a NOAA Hurricane Hunter research flight into Hurricane Sam. Dropsonde data in both the southeast and northwest quadrants indicate that small eyewall mesovortices and possibly even tornado-scale vortices were present based on the wind profiles showing sharply opposite-direction winds from what would normally be expected in those regions of the hurricane. Some dropsonde surface winds have been as high as 162 kt, which is more representative of a gust, while SFMR surface winds have been as high as 133 kt. However, the strongest 700-mb flight-level winds have been 138-139 kt in the northeastern quadrant, which equates to about 125-kt tangential surface winds. Three dropsondes released in the eye indicate that the pressure had remained steady at 943-944 mb during the duration of the aircraft reconnoiter. That pressure equates to about 125 kt based on various pressure-wind relationships. Based on that estimate and the 700-mb flight-level to surface-wind conversion, the advisory intensity is 125 kt, which is representative of the mean tangential winds and no localized wind perturbations.The initial motion is toward the west-northwest, or 295/07 kt.  Not to sound like a broken record, but no significant changes were made to the previous track forecast and reasoning. Sam is expected to move slowly west-northwestward and northwestward over the next few days around the southwestern periphery of a deep-layer subtropical ridge that is situated to the north and northeast of the small hurricane. On days 4 and 5, an upper-level trough/low is forecast to dig southward and amplify off the U.S. east coast and extend all the way to the Bahamas. This feature should act to lift Sam northward at a faster forward speed. The latest NHC model guidance based on 12Z and 18Z model runs has shifted noticeably to the east of the previous runs, and the new NHC track forecast has been nudged in that direction as well. However, since the NOAA G-IV jet aircraft has been out there sampling the environment around Sam, it's best to remain conservative and not shift the track any farther to the east until the new 00Z model runs with that new aircraft data come in for the next advisory package at 0600Z. The new NHC track forecast lies about halfway between the previous advisory track on the left and the tightly packed consensus track models on the right.The radar images from the reconnaissance aircraft indicated that the eyewall was thin in many locations due to dry-air intrusions, and the latest SHIPS intensity output indicates that Sam will remain within a fairly dry mid-level environment. Also, the depth of the warm water beneath the hurricane isn't overly deep, which could result in cold upwelling owing to Sam's slow forward motion of only 5-7 kt during the next couple of days. Eyewall replacement cycles are also likely now due to the hurricane's small size and strong intensity. Thus, fluctuations in intensity seem likely for the next couple of days even though the vertical wind shear is expected to remain quite low at only 5-10 kt. On days 3-5, however, the shear is forecast to increase to 15-20 kt from the southwest, which is expected to induce a slow weakening trend. However, it is likely that Sam will remain a major hurricane through 120 h, even on days 3-5 due to the cyclone moving over warmer and deeper water during that 3-day period. The new official intensity forecast is essentially the same as the previous advisory, and remains above the consensus model and is near the higher end of the intensity guidance.FORECAST POSITIONS AND MAX WINDSINIT  26/0300Z 13.5N  49.0W  125 KT 145 MPH12H  26/1200Z 14.0N  49.9W  130 KT 150 MPH24H  27/0000Z 14.7N  51.0W  125 KT 145 MPH36H  27/1200Z 15.4N  52.1W  120 KT 140 MPH48H  28/0000Z 16.3N  53.2W  120 KT 140 MPH60H  28/1200Z 17.1N  54.3W  115 KT 130 MPH72H  29/0000Z 18.0N  55.6W  115 KT 130 MPH96H  30/0000Z 20.1N  58.5W  110 KT 125 MPH120H  01/0000Z 23.7N  61.4W  110 KT 125 MPH$$Forecaster Stewart

 

 

Yeah I get the suspect meso/microvortices directtional changes and the 700mb 10% reduction but there was plenty of redundant data to support 130-135 kts / 155 mph on the advisory package. Either way, still an impressively intense Category 4 Cape Verde hurricane.

I’d set it at 130 kt/150 mph and threw out the P/W relationship in leu of having direct in-situ data (I.e, Recon).  Very surprised to see “Stewart” going with the conservative estimate, being he’s typically the HWRF of NHC f’casters. 

[yoda]

BULLETIN
Hurricane Sam Advisory Number  15
NWS National Hurricane Center Miami FL       AL182021
500 AM AST Sun Sep 26 2021

...SAM REMAINS A CATEGORY FOUR HURRICANE...
...FLUCTUATIONS IN INTENSITY LIKELY DURING THE NEXT DAY OR SO...


SUMMARY OF 500 AM AST...0900 UTC...INFORMATION
----------------------------------------------
LOCATION...13.8N 49.7W
ABOUT 940 MI...1510 KM ESE OF THE NORTHERN LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...145 MPH...230 KM/H
PRESENT MOVEMENT...WNW OR 295 DEGREES AT 8 MPH...13 KM/H
MINIMUM CENTRAL PRESSURE...943 MB...27.85 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 13.8 North, longitude 49.7 West.  Sam is moving toward 
the west-northwest near 8 mph (13 km/h).  This general motion is 
expected to continue today, followed by a turn toward the northwest 
on Monday.  Then, a northwestward motion is forecast to continue 
through midweek.

Maximum sustained winds are near 145 mph (230 km/h) with higher 
gusts.  Sam is a category 4 hurricane on the Saffir-Simpson 
Hurricane Wind Scale.  Some fluctuations in intensity are expected 
during the next day or so.  Thereafter, some slow weakening is 
forecast.

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 90 miles (150 km).

The estimated minimum central pressure is 943 mb (27.85 inches).

[yoda]

Hurricane Sam Discussion Number  15
NWS National Hurricane Center Miami FL       AL182021
500 AM AST Sun Sep 26 2021

Sam remains a small but intense hurricane this morning, with a 
well-defined 10 n mi-wide eye. A 0500 UTC AMSR-2 microwave pass 
reveals Sam has a compact inner core of deep convection surrounding 
its eye, with curved convective bands primarily extending around the 
northern and eastern portions of the circulation. Infrared cloud top 
temperatures briefly warmed overnight in portions of Sam's central 
dense overcast, perhaps due to some intrusions of drier mid-level 
air. The 06z objective and subjective satellite estimates ranged 
from 113-127 kt, but Sam's satellite presentation has improved in 
recent infrared imagery as cloud top temperatures are cooling around 
the eye. Thus, the initial intensity is held at 125 kt for this 
advisory. NOAA aircraft are scheduled to investigate Sam later this 
afternoon, which should provide helpful information about the 
structure and intensity of the hurricane.

Sam is moving toward the west-northwest, or 295/7 kt. A deep-layer
subtropical ridge to the north and northeast of Sam should generally
steer the hurricane west-northwestward to northwestward for the next
several days. By midweek, an amplifying upper-level trough will move
off the east coast of the U.S. and dig southward over the western
Atlantic, which will erode the western extent of the steering ridge.
The deep-layer southerly flow ahead of the trough should cause Sam
to begin recurving, with a somewhat faster north-northwestward
motion forecast by day 5. The latest NHC track forecast is very
similar to the previous one and generally lies between the HFIP
corrected consensus approach (HCCA) and TVCA aids. At days 4-5,
there is more spread in the track guidance, with the ECMWF on the
far left side of the guidance envelope and the GFS on the far right.
The NHC forecast track has been nudged just slightly to the left at
96 and 120 h, but it still lies to the right of HCCA.

The hurricane will likely experience some fluctuations in intensity 
during the next day or two. On the one hand, Sam remains over warm 
sea-surface temperatures of around 28.5 deg C, with vertical wind 
shear less than 10 kt as diagnosed from the SHIPS guidance. However, 
GOES-16 water vapor imagery shows some drier mid-level air in the 
surrounding environment that may periodically entrain into the inner 
core of Sam. Additionally, the onset of an eyewall replacement cycle 
remains a distinct possibility at this stage of Sam's life cycle, 
although the latest microwave data does not suggest one is imminent. 
The official NHC intensity forecast lies on the high end of the 
guidance for the first 36-48 h of the forecast period. Thereafter, 
the NHC forecast trends closer to the HCCA and IVCN consensus aids. 
Some gradual weakening is forecast later in the period as the 
southwesterly vertical wind shear begins to increase, but Sam is 
still forecast to remain a major hurricane through the 5-day period.


FORECAST POSITIONS AND MAX WINDS

INIT  26/0900Z 13.8N  49.7W  125 KT 145 MPH
 12H  26/1800Z 14.3N  50.6W  125 KT 145 MPH
 24H  27/0600Z 15.0N  51.8W  120 KT 140 MPH
 36H  27/1800Z 15.8N  52.9W  120 KT 140 MPH
 48H  28/0600Z 16.6N  53.9W  115 KT 130 MPH
 60H  28/1800Z 17.5N  55.0W  115 KT 130 MPH
 72H  29/0600Z 18.4N  56.3W  115 KT 130 MPH
 96H  30/0600Z 20.8N  59.3W  110 KT 125 MPH
120H  01/0600Z 24.5N  62.0W  110 KT 125 MPH

$$
Forecaster Reinhart

[cptcatz]

Looks like over the past few hours it's been moving due west with even a possible wobble to the south. Wonder how long it will keep that up. 

[bluewave]

Sam joins Lorenzo in being the strongest hurricane this far to the east in the Atlantic so late in the season.

 

 

[WxFreak11]

1 hour ago, cptcatz said:

Looks like over the past few hours it's been moving due west with even a possible wobble to the south. Wonder how long it will keep that up. 

Don’t these strong storms sometimes pump the ridge. Maybe it’s a temporary movement but it does look like due west heading last few hours.

[ineedsnow]

not a single 12z hurricane model has this going west right now.. but seems like Sam is doing just that...   12z hurricane models did shift west though with towards Bermuda or even just west

[MJO812]

11 minutes ago, ineedsnow said:

not a single 12z hurricane model has this going west right now.. but seems like Sam is doing just that...   12z hurricane models did shift west though with towards Bermuda or even just west

You would think this would go more west with the NAO pumping the ridge but Sam is too strong right now.

[SnoSki14]

16 minutes ago, MJO812 said:

You would think this would go more west with the NAO pumping the ridge but Sam is too strong right now.

There's not a lot of ridging out there. 

Obviously things have changed markedly since a couple days ago.

There remains a small possibility Sam could get left behind if he stays far enough south instead of the ULL taking him OTS. 

He's really far east though, would be a miracle to get him west enough to impact the US. 

After Sam attention will shift to western Caribbean, lots of potential there heading into October. 

[Windspeed]

We're in the midrange now. EPS and the Euro op which had been flirting with the idea of the cutoff trough hugging the inland interior is no longer resolving. So at this point I think it's pretty safe to expect that whatever troughing evolution occurs, it will be too far east to bring Sam back west towards an ECONUS threat. Can't entirely rule out ECAN yet but Sam is looking like a sole threat to Bermuda. So we'll just have to see how that evolves and if Sam comes into close proximity of the island.

Sam looks really stable right now. It will be interesting to see how long the core can avoid an ERC. Forward motion is still good enough to avoid upwelling issues, but any slowdown could also induce some weakening. SSTs are still quite warm. I'm not ruling out recon finding a stronger hurricane, but it may be at peak for its life cycle.

[Windspeed]

Re: Forward motion, it does appear that Sam is slowing down. Will be interesting to see what recon find this afternoon. Upwelling may become an issue despite Sam having a relatively small core vorticity maximum. At present this is still a mighty impressive looking Atlantic hurricane.