ATL: PETER - Advisories

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ATL: PETER - Advisories

#1 Postby cycloneye » Sat Sep 18, 2021 9:59 pm

BULLETIN
Tropical Depression Sixteen Advisory Number 1
NWS National Hurricane Center Miami FL AL162021
1100 PM AST Sat Sep 18 2021

...TROPICAL DEPRESSION FORMS EAST OF THE NORTHERN LEEWARD ISLANDS...


SUMMARY OF 1100 PM AST...0300 UTC...INFORMATION
-----------------------------------------------
LOCATION...16.4N 53.1W
ABOUT 670 MI...1080 KM E OF THE NORTHERN LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...35 MPH...55 KM/H
PRESENT MOVEMENT...WNW OR 300 DEGREES AT 14 MPH...22 KM/H
MINIMUM CENTRAL PRESSURE...1008 MB...29.77 INCHES


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

Interests in the northern Leeward Islands, Virgin Islands, and
Puerto Rico should monitor the progress of this system.


DISCUSSION AND OUTLOOK
----------------------
At 1100 PM AST (0300 UTC), the center of Tropical Depression Sixteen
was located near latitude 16.4 North, longitude 53.1 West. The
depression is moving toward the west-northwest near 14 mph (22 km/h)
and this motion is expected to continue during the next few days.
On the forecast track, the depression is expected to pass to the
north of the northern Leeward Islands on Monday and Tuesday.

Maximum sustained winds are near 35 mph (55 km/h) with higher gusts.
Some strengthening is forecast, and the depression is expected to
become a tropical storm on Sunday.

The estimated minimum central pressure is 1008 mb (29.77 inches).


HAZARDS AFFECTING LAND
----------------------
RAINFALL: The outer bands of the depression could produce rainfall
totals of 1 to 3 inches across portions of the northern Leeward
Islands, including the Virgin Islands, as well as Puerto Rico later
Sunday through Tuesday. This rainfall may lead to areas of urban and
small stream flooding.

SURF: Swells generated by the depression are expected to reach the
northern Leeward Islands Sunday night and Monday. 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 500 AM AST.

$$
Forecaster Cangialosi




Tropical Depression Sixteen Discussion Number 1
NWS National Hurricane Center Miami FL AL162021
1100 PM AST Sat Sep 18 2021

Satellite images and surface observations indicate that the area of
low pressure that NHC has been monitoring to the east of the
northern Leeward Islands now has a well-defined center and
sufficiently organized deep convection to be classified a tropical
depression. The depression has a small area of deep convection near
its center and curved bands on its north and east sides. The
initial intensity is estimated to be 30 kt, but this is a little
below the latest Dvorak classifications and could be conservative.

The depression is moving west-northwestward at 12 kt. The cyclone
should continue west-northwestward at about the same pace during the
next few days as it moves in the flow on the southwest side of a
mid-level ridge. After that time, the ridge is expected to break
down and the steering currents are forecast to become weak. Not
surprisingly, the spread in the models increases around that time,
but most of the solutions show a slow turn toward the north toward
broad troughing associated with Post-Tropical Cyclone Odette. The
GFS is on the southern side of the guidance envelope and the ECMWF
on the northern side. The NHC track forecast lies between those
models near the consensus aids.

Some strengthening seems possible during the next 12 to 24 hours and
the system is expected to become a tropical storm during that time
frame. However, an increase in southerly and then southwesterly
vertical wind shear should cause the system to level off in strength
from 24 hours through the end of the forecast period. The models
are in fairly good agreement on this overall scenario, and the NHC
intensity forecast is in line with the majority of the guidance.

Based on the track, intensity, and wind radii forecast, no tropical
storm watches or warnings are required for the northern Leeward
Islands, Virgin Islands or Puerto Rico. However, interests there
should monitor the progress of the system as locally heavy rain is
possible on Monday and Tuesday when it is expected to pass to the
north of the area.


FORECAST POSITIONS AND MAX WINDS

INIT 19/0300Z 16.4N 53.1W 30 KT 35 MPH
12H 19/1200Z 17.3N 54.8W 35 KT 40 MPH
24H 20/0000Z 18.5N 57.3W 40 KT 45 MPH
36H 20/1200Z 19.4N 59.8W 40 KT 45 MPH
48H 21/0000Z 20.3N 61.9W 35 KT 40 MPH
60H 21/1200Z 21.3N 64.1W 35 KT 40 MPH
72H 22/0000Z 22.3N 65.5W 35 KT 40 MPH
96H 23/0000Z 24.4N 66.5W 35 KT 40 MPH
120H 24/0000Z 26.3N 66.2W 35 KT 40 MPH

$$
Forecaster Cangialosi
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Re: ATL: PETER - Advisories

#2 Postby cycloneye » Sun Sep 19, 2021 7:55 am

BULLETIN
Tropical Storm Peter Special Advisory Number 3
NWS National Hurricane Center Miami FL AL162021
900 AM AST Sun Sep 19 2021

...CENTER OF PETER FOUND FARTHER SOUTH AND WEST...
...STILL EXPECTED TO PASS WELL NORTH OF THE LESSER ANTILLES...


SUMMARY OF 900 AM AST...1300 UTC...INFORMATION
----------------------------------------------
LOCATION...17.6N 56.0W
ABOUT 470 MI...755 KM E OF THE NORTHERN LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...45 MPH...75 KM/H
PRESENT MOVEMENT...WNW OR 290 DEGREES AT 15 MPH...24 KM/H
MINIMUM CENTRAL PRESSURE...1008 MB...29.77 INCHES


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

Interests in the northern Leeward Islands, Virgin Islands, and
Puerto Rico should monitor the progress of this system.


DISCUSSION AND OUTLOOK
----------------------
At 900 AM AST (1300 UTC), the center of Tropical Storm Peter was
located near latitude 17.6 North, longitude 56.0 West. Peter is
moving toward the west-northwest near 15 mph (24 km/h) and this
motion is expected to continue through Wednesday. On the forecast
track, Peter is expected to pass well to the north of the northern
Leeward Islands on Monday and Tuesday.

Maximum sustained winds are near 45 mph (75 km/h) with higher gusts.
Some additional strengthening is forecast during the next day or
so, followed by a slow weakening trend by late Monday and on
Tuesday.

Tropical-storm-force winds extend outward up to 105 miles (170 km)
from the center.

The estimated minimum central pressure is 1008 mb (29.77 inches).


HAZARDS AFFECTING LAND
----------------------
RAINFALL: The outer bands south of the Tropical Storm Peter could
produce rainfall totals of 1 to 3 inches across portions of the
Northern Leeward Islands, including the Virgin Islands, as well as
Puerto Rico late Sunday into Tuesday. This rainfall may lead to
areas of urban and small stream flooding.

SURF: Swells generated by Tropical Storm Peter are expected to
reach the northern Leeward Islands Sunday night and Monday. 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.

$$
Forecaster Latto




Tropical Storm Peter Special Discussion Number 3
NWS National Hurricane Center Miami FL AL162021
900 AM AST Sun Sep 19 2021

Satellite imagery as well as data from a Air Force Reserve Hurricane
Hunter aircraft indicate that the center of Peter is over 100 n mi
west-southwest of its forecast position. Therefore, a special
advisory for track is being issued. The forecast track has been
adjusted through the first 60 h, resulting in a slight southward
adjustment of the track through the first couple of days. The
aircraft also measured 925 mb flight-level winds of 56 kt, which
supports an initial intensity of 40 kt. No adjustments were made
to the intensity forecast. The next full advisory will be issued at
1500 UTC.

Based on the track, intensity, and wind radii forecast, no tropical
storm watches or warnings are required for the northern Leeward
Islands, Virgin Islands or Puerto Rico. However, interests there
should monitor the progress of the system as locally heavy rain is
possible on Monday and Tuesday when it is expected to pass to the
north of the area.

Key Messages:

1. Rainfall around the southern periphery of Tropical Storm Peter
may lead to areas of urban and small stream flooding from late
Sunday into Tuesday across Puerto Rico, the Virgin Islands, and the
Northern Leeward Islands.


FORECAST POSITIONS AND MAX WINDS

INIT 19/1300Z 17.6N 56.0W 40 KT 45 MPH
12H 19/1800Z 18.2N 57.0W 40 KT 45 MPH
24H 20/0600Z 19.3N 58.8W 40 KT 45 MPH
36H 20/1800Z 20.2N 61.1W 40 KT 45 MPH
48H 21/0600Z 21.3N 63.2W 35 KT 40 MPH
60H 21/1800Z 22.6N 65.0W 35 KT 40 MPH
72H 22/0600Z 24.3N 65.6W 35 KT 40 MPH
96H 23/0600Z 25.8N 65.6W 35 KT 40 MPH
120H 24/0600Z 27.7N 65.2W 35 KT 40 MPH

$$
Forecaster Latto
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Re: ATL: PETER - Advisories

#3 Postby cycloneye » Sun Sep 19, 2021 11:42 am

BULLETIN
Tropical Storm Peter Advisory Number 4
NWS National Hurricane Center Miami FL AL162021
1100 AM AST Sun Sep 19 2021

...DISHEVELED PETER HEADING WEST-NORTHWESTWARD...
...EXPECTED TO PASS NORTH OF THE LESSER ANTILLES EARLY THIS WEEK...


SUMMARY OF 1100 AM AST...1500 UTC...INFORMATION
-----------------------------------------------
LOCATION...17.6N 56.5W
ABOUT 435 MI...700 KM E OF THE NORTHERN LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...45 MPH...75 KM/H
PRESENT MOVEMENT...WNW OR 290 DEGREES AT 17 MPH...28 KM/H
MINIMUM CENTRAL PRESSURE...1007 MB...29.74 INCHES


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

Interests in the northern Leeward Islands, Virgin Islands, and
Puerto Rico should monitor the progress of this system.


DISCUSSION AND OUTLOOK
----------------------
At 1100 AM AST (1500 UTC), the center of Tropical Storm Peter was
located near latitude 17.6 North, longitude 56.5 West. Peter is
moving toward the west-northwest near 17 mph (28 km/h), and this
general motion along with a gradual decrease in forward speed is
is expected through Tuesday. A turn to the northwest is expected
to occur by Wednesday. On the forecast track, the center of Peter
is expected to pass well north of the Leeward Islands on Monday and
Tuesday.

Based on data from a Air Force Reserve Hurricane Hunter aircraft,
maximum sustained winds remain near 45 mph (75 km/h) with higher
gusts. Little change in strength is forecast through today. Some
slight weakening is expected tonight into Monday.

Tropical-storm-force winds extend outward up to 115 miles (185 km),
primarily northeast of the center.

The estimated minimum central pressure based on the aircraft data
is 1007 mb (29.74 inches).


HAZARDS AFFECTING LAND
----------------------
RAINFALL: The outer bands south of the tropical storm could produce
rainfall totals of 1 to 3 inches with locally higher amounts
possible across portions of the Northern Leeward Islands, including
the Virgin Islands, as well as Puerto Rico late today through
Tuesday. This rainfall may lead to areas of urban and small stream
flooding.

SURF: Swells generated by Tropical Storm Peter are expected to
reach the northern Leeward Islands tonight and Monday. 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 500 PM AST.

$$
Forecaster Latto

Tropical Storm Peter Discussion Number 4
NWS National Hurricane Center Miami FL AL162021
1100 AM AST Sun Sep 19 2021

Earlier this morning, Peter began to encounter increasing
southwesterly shear emanating from flow around an upper-level
trough to its northwest. This shear caused the low-level center of
the storm to separate from the deep convection and as of now is
located over 100 n mi from the edge of that band of convection. An
Air Force Reserve Hurricane Hunter aircraft has been investigating
the cyclone for the past few hours and has provided helpful data on
the structure and intensity of Peter. Based on the aircraft data,
tropical-storm-force winds extend at least 100 n mi to the northeast
of the center, while there are no tropical-storm-force winds in the
southern semicircle. The initial intensity of 40 kt is based on
aircraft passes through the northeastern quadrant that measured
peak 925 mb flight-level winds of 56 and 54 kt.

The initial motion is 290/15 kt. Peter is forecast to continue to
move in this west-northwestward direction for the next couple of
days as it is steered to the south of a subtropical ridge. This
ridge is expected to weaken in a few days which should cause the
cyclone to turn northwestward. Late in the forecast period a turn to
the north and possibly northeast is expected to occur as Peter gets
caught in the flow around a large trough to its north. As mentioned
in the special advisory discussion a couple hours ago, a shift to
the west-southwest of the track was required to accommodate a
initial position adjustment. Some additional southward adjustments
were made to the official NHC track for this advisory to come into
better agreement with a blend of the GFS/ECMWF solutions that also
indicate a shallower system.

The UW-CIMSS shear analysis suggests about 20 kt of southwesterly
shear is impacting Peter. Just to its west and northwest, where the
cyclone is heading, the shear is analyzed as 30 kt or greater.
Given that Peter is already exhibiting the structure of a highly
sheared tropical cyclone, some slight weakening is now forecast
tonight into tomorrow. There is quite a bit of spread in the
environmental forecast between the GFS and ECMWF beyond day 3, as
the GFS shows shear increasing to 40 kt, while the ECMWF indicates
a less hostile environment with 20 kt of shear. Assuming Peter
survives its interaction with the upper trough to its northwest
over the next few days, additional weakening is indicated
due to the ongoing shear. It should be noted that quite a few GFS
ensemble members open Peter into a trough by the end of the
forecast period. The latest NHC intensity forecast is near the
various consensus solutions. However, due to the possibility the
cyclone may not survive the next few days, the confidence in this
forecast is lower than normal.

Based on the track, intensity, and wind radii forecast, no tropical
storm watches or warnings are required for the northern Leeward
Islands, Virgin Islands or Puerto Rico. However, interests there
should monitor the progress of the system as locally heavy rain is
possible on Monday and Tuesday when it is expected to pass to the
north of the area.


Key Messages:

1. Rainfall around the southern periphery of Tropical Storm Peter
may lead to areas of urban and small stream flooding from late today
into Tuesday across Puerto Rico, the Virgin Islands, and the
Northern Leeward Islands.


FORECAST POSITIONS AND MAX WINDS

INIT 19/1500Z 17.6N 56.5W 40 KT 45 MPH
12H 20/0000Z 18.3N 58.6W 40 KT 45 MPH
24H 20/1200Z 19.2N 60.8W 35 KT 40 MPH
36H 21/0000Z 20.2N 63.0W 35 KT 40 MPH
48H 21/1200Z 21.3N 64.9W 35 KT 40 MPH
60H 22/0000Z 22.5N 66.3W 35 KT 40 MPH
72H 22/1200Z 23.8N 67.0W 35 KT 40 MPH
96H 23/1200Z 25.5N 67.4W 30 KT 35 MPH
120H 24/1200Z 27.2N 66.7W 30 KT 35 MPH

$$
Forecaster Latto
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Re: ATL: PETER - Advisories

#4 Postby cycloneye » Sun Sep 19, 2021 4:15 pm

BULLETIN
Tropical Storm Peter Advisory Number 5
NWS National Hurricane Center Miami FL AL162021
500 PM AST Sun Sep 19 2021

...PETER FENDING OFF STRONG WIND SHEAR...
...EXPECTED TO PASS NORTH OF THE LESSER ANTILLES EARLY THIS WEEK...


SUMMARY OF 500 PM AST...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...18.4N 57.8W
ABOUT 350 MI...560 KM E OF THE NORTHERN LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...45 MPH...75 KM/H
PRESENT MOVEMENT...WNW OR 290 DEGREES AT 17 MPH...28 KM/H
MINIMUM CENTRAL PRESSURE...1007 MB...29.74 INCHES


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

Interests in the northern Leeward Islands, Virgin Islands, and
Puerto Rico should monitor the progress of this system.


DISCUSSION AND OUTLOOK
----------------------
At 500 PM AST (2100 UTC), the center of Tropical Storm Peter was
located near latitude 18.4 North, longitude 57.8 West. Peter is
moving toward the west-northwest near 17 mph (28 km/h), and this
general motion along with a gradual decrease in forward speed is
is expected through Tuesday. A turn to the northwest is expected
to occur by Wednesday. On the forecast track, the center of Peter
is expected to pass well north of the Leeward Islands on Monday and
Tuesday.

Maximum sustained winds are near 45 mph (75 km/h) with higher
gusts. Little change in strength is forecast tonight. Some slight
weakening is expected on Monday.

Tropical-storm-force winds extend outward up to 125 miles (205 km)
primarily to the northeast of the center.

The estimated minimum central pressure is 1007 mb (29.74 inches).


HAZARDS AFFECTING LAND
----------------------
RAINFALL: Rainfall around the southern periphery of Tropical Storm
Peter could produce rainfall totals of 1 to 3 inches, with locally
higher amounts possible, across portions of the Northern Leeward
Islands, including the Virgin Islands, as well as Puerto Rico
through Tuesday. This rainfall may lead to areas of urban and small
stream flooding.

SURF: Swells generated by Tropical Storm Peter are expected to
reach the northern Leeward Islands tonight and Monday, and then the
Bahamas by midweek. 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 PM AST.

$$
Forecaster Latto




Tropical Storm Peter Discussion Number 5
NWS National Hurricane Center Miami FL AL162021
500 PM AST Sun Sep 19 2021

Over the past few hours deep convection with cloud tops as cold as
-85 degrees C have developed near and to the east of the center of
Peter. An Air Force Reserve Hurricane Hunter aircraft investigating
the system earlier provided data during several legs of the flight
that confirmed an intensity of 40 kt. A blend of the latest Dvorak
T- and CI- numbers from TAFB are consistent with that data, and
therefore the initial intensity remains 40 kt for this advisory.

The vertical wind shear that stripped Peter of its deep convection
earlier today is forecast to increase further through tonight and
persist for at least a few days. Global model simulated satellite
imagery suggests this latest burst of convection will also become
removed from the center within several hours, with the cyclone
struggling to maintain persistent deep convection throughout much of
the 5-day forecast period. Therefore, despite being over very warm
waters, Peter is forecast to slowly weaken over the next several
days. The intensity model guidance is in decent agreement on this
scenario, and the NHC forecast remains near the various intensity
consensus solutions. As mentioned in the previous discussion, there
are some indications, particularly by the GFS, that Peter could open
back into a wave within a few days which adds some additional
uncertainty to the intensity forecast.

Peter's initial motion remains 290/15 kt. The storm is forecast to
continue to move in this west-northwestward direction for the next
couple of days as it is steered to the south of a subtropical ridge.
This ridge is expected to weaken in a few days which should cause
the cyclone to slow its forward motion and turn northwestward. Late
in the forecast period a turn to the north and possibly northeast
is expected to occur as Peter gets caught in the flow around a
large trough to its north. The model guidance has shifted westward
beyond day 2, in part due to a faster forward motion. While the
timing of the cyclone's turn to the north remains the same, the NHC
forecast was shifted to the left beyond 48 h, but still remains to
the east of the consensus.

Based on the track, intensity, and wind radii forecast, no tropical
storm watches or warnings are required for the northern Leeward
Islands, Virgin Islands or Puerto Rico. However, interests there
should monitor the progress of the system as locally heavy rain is
possible on Monday and Tuesday when it is expected to pass to the
north of the area.


Key Messages:

1. Rainfall around the southern periphery of Tropical Storm Peter
may lead to areas of urban and small stream flooding from late today
into Tuesday across Puerto Rico, the Virgin Islands, and the
Northern Leeward Islands.


FORECAST POSITIONS AND MAX WINDS

INIT 19/2100Z 18.4N 57.8W 40 KT 45 MPH
12H 20/0600Z 19.1N 59.8W 40 KT 45 MPH
24H 20/1800Z 19.9N 62.1W 35 KT 40 MPH
36H 21/0600Z 20.8N 64.3W 35 KT 40 MPH
48H 21/1800Z 21.9N 66.0W 35 KT 40 MPH
60H 22/0600Z 22.9N 67.2W 35 KT 40 MPH
72H 22/1800Z 24.1N 68.2W 30 KT 35 MPH
96H 23/1800Z 26.1N 68.3W 30 KT 35 MPH
120H 24/1800Z 27.7N 67.5W 30 KT 35 MPH

$$
Forecaster Latto
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Re: ATL: PETER - Advisories

#5 Postby cycloneye » Sun Sep 19, 2021 10:00 pm

BULLETIN
Tropical Storm Peter Advisory Number 6
NWS National Hurricane Center Miami FL AL162021
1100 PM AST Sun Sep 19 2021

...AIR FORCE HURRICANE HUNTERS FIND PETER A LITTLE STRONGER...
...PETER EXPECTED TO PASS NORTH OF THE LEEWARD ISLANDS EARLY THIS
WEEK...


SUMMARY OF 1100 PM AST...0300 UTC...INFORMATION
-----------------------------------------------
LOCATION...18.6N 58.5W
ABOUT 305 MI...485 KM E OF THE NORTHERN LEEWARD ISLANDS
MAXIMUM SUSTAINED WINDS...50 MPH...85 KM/H
PRESENT MOVEMENT...WNW OR 295 DEGREES AT 14 MPH...22 KM/H
MINIMUM CENTRAL PRESSURE...1004 MB...29.65 INCHES


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

Interests in the northern Leeward Islands, Virgin Islands, and
Puerto Rico should monitor the progress of this system.


DISCUSSION AND OUTLOOK
----------------------
At 1100 PM AST (0300 UTC), the center of Tropical Storm Peter was
located near latitude 18.6 North, longitude 58.5 West. Peter is
moving toward the west-northwest near 14 mph (22 km/h). This
general motion is expected to continue during the next couple of
days, followed by a turn to the northwest with a decrease in
forward speed on Wednesday.

Data from an Air Force Reserve Hurricane Hunter aircraft indicate
that maximum sustained winds have increased to near 50 mph (85 km/h)
with higher gusts. Some gradual weakening is forecast during the
next several days.

Tropical-storm-force winds extend outward up to 140 miles (220 km)
primarily to the northeast of the center.

The estimated minimum central pressure is 1004 mb (29.65 inches).


HAZARDS AFFECTING LAND
----------------------
RAINFALL: Rainfall around the southern periphery of Tropical Storm
Peter could produce rainfall totals of 1 to 3 inches, with locally
higher amounts possible, across portions of the Northern Leeward
Islands, including the Virgin Islands, as well as Puerto Rico
through Tuesday. This rainfall may lead to areas of urban and small
stream flooding.

SURF: Swells generated by Peter are expected to affect the northern
Leeward Islands early this week, and then reach the Bahamas by
midweek. 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 500 AM AST.

$$
Forecaster Reinhart




Tropical Storm Peter Discussion Number 6
NWS National Hurricane Center Miami FL AL162021
1100 PM AST Sun Sep 19 2021

Peter is a sheared tropical cyclone. Satellite imagery and microwave
data indicate that an earlier convective burst near the center of
Peter has collapsed tonight. Although the low-level center is now
displaced at least 60 n mi west of the edge of the convective cloud
mass, an Air Force Reserve Hurricane Hunter aircraft investigating
Peter has found the cyclone is a bit stronger tonight. The aircraft
measured flight-level (925 mb) winds of 58 kt and SFMR winds of 45
kt or so. These data support raising the initial intensity to 45 kt
for this advisory.

Peter's wind field is very asymmetric, with tropical-storm-force
winds extending outward up to 120 n mi from the center only in its
northeast quadrant. The moderate to strong southwesterly vertical
wind shear that is plaguing the system is forecast to persist during
the next several days. Thus, despite sufficient oceanic heat content
along its forecast track, the official NHC intensity forecast does
not show any further intensification. In fact, some gradual
weakening is forecast since the system appears likely to struggle
sustaining organized convection near its center, as suggested by
GFS and ECMWF model simulated satellite imagery. The official NHC
intensity forecast has been adjusted upward in the near-term to
account for the stronger initial intensity, but otherwise closely
follows the HCCA and IVCN aids and shows gradual weakening this
week. While the official NHC forecast shows Peter remaining a
tropical cyclone through the forecast period, the GFS suggests
Peter could struggle to even maintain its closed low-level
circulation in the coming days. Therefore, it is plausible that the
cyclone could degenerate into an open wave and weaken somewhat
quicker than forecast.

Peter is moving west-northwestward, or 295/12 kt, along the
southwestern periphery of a subtropical ridge over the central
Atlantic. This general motion should continue for the next couple of
days. Thereafter, the track forecast becomes more challenging. A
low- to mid-level ridge is expected to build over the western
Atlantic by midweek, which would keep the weakening cyclone on a
more northwestward trajectory. But, a mid-level shortwave is
forecast to drop southward and erode the southern extent of the
ridge, which should eventually draw Peter more northward during the
middle and latter parts of the week. There is more spread noted in
the track guidance at days 3-5, as the timing of this northward turn
is uncertain. The official NHC track forecast has been adjusted
slightly to the left of the previous one, and it lies near the
center of the guidance envelope and closer to the TVCA and HCCA
aids.

Based on the latest track, intensity, and wind radii forecasts, no
tropical storm watches or warnings are required for the northern
Leeward Islands, Virgin Islands, or Puerto Rico at this time.
However, locally heavy rain is possible on Monday and Tuesday when
Peter is expected to pass to the north of these locations.


Key Messages:

1. Rainfall around the southern periphery of Tropical Storm Peter
may lead to areas of urban and small stream flooding through Tuesday
across Puerto Rico, the Virgin Islands, and the Northern Leeward
Islands.


FORECAST POSITIONS AND MAX WINDS

INIT 20/0300Z 18.6N 58.5W 45 KT 50 MPH
12H 20/1200Z 19.3N 60.6W 40 KT 45 MPH
24H 21/0000Z 20.1N 62.9W 40 KT 45 MPH
36H 21/1200Z 21.0N 65.0W 35 KT 40 MPH
48H 22/0000Z 22.0N 66.7W 35 KT 40 MPH
60H 22/1200Z 23.0N 67.9W 30 KT 35 MPH
72H 23/0000Z 23.9N 68.6W 30 KT 35 MPH
96H 24/0000Z 25.7N 68.5W 25 KT 30 MPH
120H 25/0000Z 28.0N 67.5W 25 KT 30 MPH

$$
Forecaster Reinhart
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Re: ATL: PETER - Advisories

#6 Postby cycloneye » Mon Sep 20, 2021 3:58 am

Tropical Storm Peter Discussion Number 7...Corrected
NWS National Hurricane Center Miami FL AL162021
500 AM AST Mon Sep 20 2021

Corrected name of storm in first and second paragraphs

Peter is a strongly sheared tropical storm. Reconnaissance wind
data, conventional satellite imagery, and passive microwave
satellite data indicate that Peter's center is located just to the
west of the deep convection. Data from the aircraft support holding
the intensity at 45 kt for now based on 925-mb flight-level and
SFMR winds of 53 kt and 41 kt, respectively, on their last leg when
the aircraft came in from the northeast. The central pressure had
also increased only slightly to 1006 mb.

Peter has continued to move west-northwestward, or 295/12 kt. There
are no significant changes to the previous track forecast or
reasoning. Peter is expected to move around the southwestern and
western periphery of a subtropical ridge for the next couple of
days, followed by a slow northward motion on days 3-5 as the
cyclone moves through a weakness in the ridge induced by the
southward-moving former Tropical Storm Odette. The new NHC track
forecast is very similar to the previous advisory track, and lies
just to the east of the tightly packed consensus track models.

Some fluctuations in intensity will be possible during the next
24-36 hours owing to 5-10 kt fluctuations in the magnitude and also
the direction of the deep-layer vertical wind shear. However, by 48
hours and beyond, a slow weakening trend is expected due to the
shear increasing from the southwest and west-southwest of near 30
kt. The new official intensity forecast is essentially just an
update of the previous advisory, and closely follows the IVCN and
HCCA intensity consensus models.

Based on the latest track, intensity, and wind radii forecasts, no
tropical storm watches or warnings are required for the northern
Leeward Islands, Virgin Islands, or Puerto Rico at this time.
However, locally heavy rain is possible on Monday and Tuesday when
Peter is expected to pass to the north of these locations.


Key Messages:

Rainfall around the southern periphery of Tropical Storm Peter may
lead to areas of urban and small stream flooding through Tuesday
across Puerto Rico, the Virgin Islands, and the Northern Leeward
Islands.


FORECAST POSITIONS AND MAX WINDS

INIT 20/0900Z 19.1N 59.5W 45 KT 50 MPH
12H 20/1800Z 19.7N 61.4W 40 KT 45 MPH
24H 21/0600Z 20.4N 63.6W 40 KT 45 MPH
36H 21/1800Z 21.4N 65.5W 35 KT 40 MPH
48H 22/0600Z 22.4N 67.2W 35 KT 40 MPH
60H 22/1800Z 23.2N 68.0W 30 KT 35 MPH
72H 23/0600Z 24.2N 68.4W 30 KT 35 MPH
96H 24/0600Z 26.2N 67.8W 25 KT 30 MPH
120H 25/0600Z 28.5N 66.8W 30 KT 35 MPH

$$
Forecaster Stewart
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cycloneye
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Re: ATL: PETER - Advisories

#7 Postby cycloneye » Mon Sep 20, 2021 9:52 am

Tropical Storm Peter Discussion Number 8
NWS National Hurricane Center Miami FL AL162021
1100 AM AST Mon Sep 20 2021

West-southwesterly vertical wind shear on the order of 30 kt is
pummeling Peter this morning. Just like yesterday morning, the
low-level center of the storm is pulling away from the deep
convection and is now displaced greater than 80 n mi. An Air Force
Reserve Hurricane Hunter aircraft has been investigating Peter this
morning and has measured peak 925-mb flight-level winds of 54 kt
and several SFMR values of 40-45 kt, supporting keeping the initial
intensity at 45 kt for this advisory.

Peter refuses to slow down, and for the past several hours has been
moving 290/14 kt. This west-northwestward motion is forecast to
continue for the next two days as the system remains to the
southwest of a subtropical ridge. By Wednesday, Peter should slow
down and turn northwest then north as it reaches a developing
weakness in the ridge carved out by a mid-latitude trough
moving across the northeastern United States later this week. The
model track guidance has shifted slightly left for the 24-72 h time
frames, and the NHC forecast track was nudged in that direction as
well. Otherwise, the latest NHC forecast track is little changed
from the previous one.

An upper-level trough to the west of Peter is forecast to remain
near the cyclone for the next few days, keeping the storm in a
high-shear environment. Therefore, despite being over warm waters
the storm is forecast to slowly weaken. If Peter survives the next
72 h, there could be a window of opportunity late in the forecast
period for some modest strengthening as the cyclone would have
lifted to the north of the upper trough. It should be noted that a
vast majority of the GFS ensembles show Peter dissipating later this
week as the system opens into a wave. This scenario is plausible,
especially if deep convection fails to persist near the center of
the cyclone. The latest NHC intensity forecast assumes Peter
survives, and closely follows the various intensity consensus
solutions.

Based on the latest track, intensity, and wind radii forecasts, no
tropical storm watches or warnings are required for the northern
Leeward Islands, Virgin Islands, or Puerto Rico at this time.
However, locally heavy rain is possible today and Tuesday when
Peter is expected to pass to the north of these locations.


Key Messages:

1. Rainfall around the southern periphery of Tropical Storm Peter
may lead to areas of urban and small stream flooding through
Tuesday across northern Hispaniola, Puerto Rico, the Virgin
Islands, and the Northern Leeward Islands.


FORECAST POSITIONS AND MAX WINDS

INIT 20/1500Z 19.5N 60.9W 45 KT 50 MPH
12H 21/0000Z 20.1N 62.7W 40 KT 45 MPH
24H 21/1200Z 20.8N 64.8W 40 KT 45 MPH
36H 22/0000Z 21.8N 66.6W 35 KT 40 MPH
48H 22/1200Z 22.7N 67.9W 35 KT 40 MPH
60H 23/0000Z 23.5N 68.6W 30 KT 35 MPH
72H 23/1200Z 24.5N 68.7W 30 KT 35 MPH
96H 24/1200Z 26.5N 67.6W 30 KT 35 MPH
120H 25/1200Z 28.6N 66.4W 35 KT 40 MPH

$$
Forecaster Latto
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