老農民版夜神月

  四級颶風  
編號：18 L
名稱：Sam

  基本資料  
擾動編號日期：2021 年 09 月 20 日 14 時
命名日期　　：2021 年 09 月 23 日 21 時
撤編日期　　：2021 年 10 月 06 日 20 時
登陸地點　　：無

  巔峰時期資料  
近中心最強風速 ：135  kt ( Cat.4 )
海平面最低氣壓 ：938 百帕

  擾動編號資料  
98L.INVEST.25kts.1007mb.9.5N.19.3W


  NHC：10%

1. A tropical wave located over the far eastern tropical Atlantic
several hundred miles southeast of the Cabo Verde Islands is
producing an area of disorganized showers and thunderstorms.  
Environmental conditions appear conducive for gradual development
over the next several days, and a tropical depression could form
later this week while the system moves westward at 10 to 15 mph
across the eastern and central tropical Atlantic Ocean.
* Formation chance through 48 hours...low...10 percent.
* Formation chance through 5 days...medium...60 percent.

以上資料來自：NHC、颱風論壇整理製作

king111807

NHC展望升至20%

1. A tropical wave located over the far eastern tropical Atlantic
several hundred miles south-southeast of the Cabo Verde Islands
is producing an area of showers and thunderstorms that are showing
some signs of organization.  Upper-level winds are expected to
become more conducive for further development by midweek, and a
tropical depression is likely to form by Friday while the system
moves westward at 10 to 15 mph across the eastern and central
tropical Atlantic Ocean.
* Formation chance through 48 hours...low...20 percent.
* Formation chance through 5 days...high...70 percent.

king111807

NHC展望升至30%

1. Showers and thunderstorms associated with a tropical wave located
several hundred miles south of the Cabo Verde Islands are
still showing some signs of organization, although there does not
appear to be a surface circulation at this time.  Upper-level
winds, however, are expected to become conducive for further
development by midweek, and a tropical depression is likely to form
by Thursday or Friday while the system moves westward at 10 to 15
mph across the eastern and central tropical Atlantic Ocean.
* Formation chance through 48 hours...low...30 percent.
* Formation chance through 5 days...high...80 percent.

king111807

NHC展望升至Medium，50%

1. Showers and thunderstorms associated with a tropical wave located a
few hundred miles south-southwest of the Cabo Verde Islands continue
to show some signs of organization. Environmental conditions are
expected to become more conducive for development, and a tropical
depression is likely to form later this week while the system moves
westward at 10 to 15 mph across the eastern and central tropical
Atlantic Ocean.
* Formation chance through 48 hours...medium...50 percent.
* Formation chance through 5 days...high...80 percent.

霧峰追風者

1. Showers and thunderstorms associated with a tropical wave located
several hundred miles southwest of the Cabo Verde Islands have
increased since this morning and are beginning to show signs of
organization. Recent satellite wind data also indicate that a broad
area of low pressure has formed, but the system lacks a well-defined
center. Environmental conditions are expected to remain conducive
for additional development, and a tropical depression is likely to
form within the next day or two while the system moves westward at
10 to 15 mph across the eastern and central tropical Atlantic Ocean.
* Formation chance through 48 hours...high...80 percent.
* Formation chance through 5 days...high...90 percent.

king111807

FWC-N發布TCFA

SUBJ/TROPICAL CYCLONE FORMATION ALERT (98L)//
WTNT21 KNGU 220100
RMKS/1. FORMATION OF A SIGNIFICANT TROPICAL CYCLONE IS POSSIBLE
WITHIN 100 NM EITHER SIDE OF A LINE FROM 9.7N 29.5W TO 9.8N 34.8W
WITHIN THE NEXT 24 HOURS. AVAILABLE DATA DOES NOT JUSTIFY
ISSUANCE OF NUMBERED TROPICAL CYCLONE WARNINGS AT THIS TIME. WINDS
IN THE AREA ARE ESTIMATED TO BE 20 TO 25 KNOTS. METSAT IMAGERY,
SYNOPTIC DATA AND RADAR DATA AT 212330Z INDICATE THAT A CIRCULATION
CENTER IS LOCATED NEAR 9.7N 29.5W. THE SYSTEM IS MOVING WESTWARD AT
15 KNOTS.
2. SHOWERS AND THUNDERSTORMS ASSOCIATED WITH A TROPICAL WAVE LOCATED
SEVERAL HUNDRED MILES SOUTHWEST OF THE CABO VERDE ISLANDS HAVE
INCREASED SINCE THIS MORNING AND ARE BEGINNING TO SHOW SIGNS OF
ORGANIZATION. RECENT SATELLITE WIND DATA ALSO INDICATE THAT A BROAD
AREA OF LOW PRESSURE HAS FORMED, BUT THE SYSTEM LACKS A WELL-DEFINED
CENTER. ENVIRONMENTAL CONDITIONS ARE EXPECTED TO REMAIN CONDUCIVE
FOR ADDITIONAL DEVELOPMENT, AND A TROPICAL DEPRESSION IS LIKELY TO
FORM WITHIN THE NEXT DAY OR TWO WHILE THE SYSTEM MOVES WESTWARD AT
10 TO 15 MPH ACROSS THE EASTERN AND CENTRAL TROPICAL ATLANTIC OCEAN.
3. THIS ALERT WILL BE REISSUED, UPGRADED TO WARNING OR CANCELLED BY
230100Z.//

king111807

NHC展望升至100%

1. Showers and thunderstorms remain well organized in association with
a tropical wave located several hundred miles southwest of the Cabo
Verde Islands. In addition, recent satellite wind data indicates
that the circulation is gradually becoming better defined. If these
trends continue, a tropical depression could form as soon as this
afternoon or evening. This system should move westward at 10 to 15
mph across the eastern and central tropical Atlantic Ocean.
Additional information on this system, including gale warnings, can
be found in High Seas Forecasts issued by the National Weather
Service.
* Formation chance through 48 hours...high...near 100 percent.
* Formation chance through 5 days...high...near 100 percent.

king111807

NHC升格TD18L

WTNT43 KNHC 222054
TCDAT3

Tropical Depression Eighteen Discussion Number   1
NWS National Hurricane Center Miami FL       AL182021
500 PM AST Wed Sep 22 2021

The tropical wave that NHC has been monitoring over the last several
days has gradually become better organized. The satellite structure
in particular is quite impressive for a tropical depression, with
both the 1800 UTC subjective Dvorak estimates from TAFB and SAB
at T2.5/35 kt. This bigger question, however, was if the system
possessed a well-defined closed earth-relative circulation. An
ASCAT-C pass from earlier this morning hinted that the circulation
was becoming better defined, with the development of westerly
low-level winds to the south of the convective shield. This westerly
low-level flow is also confirmed by atmospheric motion vectors
(AMVs) available from the GOES-16 meso domain over the system. While
the low-level circulation may still be somewhat broad, it now
appears to be well-defined enough to mark the formation of a
tropical cyclone. The initial intensity is set at 30-kt, in
agreement with peak wind retrievals of 28-30 kt by the earlier
scatterometer data.  

The initial motion is estimated to be at 270/13 kt, though this is
somewhat uncertain given that the center has only recently formed.
An expansive mid-level ridge is located to the north and west of
the cyclone, which should maintain its heading toward the west,
though with a gradual gain in latitude as the system approaches
the western extent of the ridge by day 5. The track guidance is in
excellent agreement on this track evolution for the first three
days, with just a bit more spread in the guidance thereafter. The
ECMWF and its ensemble mean towards the end of the forecast is on
the left side of the guidance envelope, while the GFS and HWRF
models are currently on the right side. For the first NHC track
forecast, I have elected to stay close to the track consensus aids,
taking a blend of the HCCA and TCVN aids which are near the
middle of the guidance envelope.

The environment ahead of the tropical depression appears quite
favorable for intensification. Vertical wind shear is forecast by
both the ECWMF- and GFS-based SHIPS guidance to stay at or under 10
kt for the next 3-5 days as the storm traverses warm 28-29 C sea
surface temperatures. Most of the guidance responds to this
environment by indicating strengthening, and the NHC intensity
guidance follows suit, showing a steady increase in intensity
throughout the forecast period. While it might take a bit of time
for the formative low-level circulation to become vertically aligned
with the mid-level center, once that occurs, it is possible a period
of rapid intensification could occur during the five day forecast.
The forecast intensity by 120 hours (100 kt) is on the higher end of
the guidance envelope, but not as high as the latest HWRF or HAFS-B
forecasts.

FORECAST POSITIONS AND MAX WINDS

INIT  22/2100Z 10.1N  33.9W   30 KT  35 MPH
12H  23/0600Z 10.1N  36.0W   35 KT  40 MPH
24H  23/1800Z 10.5N  38.6W   40 KT  45 MPH
36H  24/0600Z 11.0N  41.1W   50 KT  60 MPH
48H  24/1800Z 11.7N  43.4W   60 KT  70 MPH
60H  25/0600Z 12.4N  45.3W   70 KT  80 MPH
72H  25/1800Z 13.0N  46.8W   80 KT  90 MPH
96H  26/1800Z 14.2N  49.5W   90 KT 105 MPH
120H  27/1800Z 16.0N  52.5W  100 KT 115 MPH

$$
Forecaster Papin