Tropical Storm Peter

Post Tropical Peter Track 2300 Hours Septemberf 22 2021
Post Tropical Peter Track 2300 Hours Septemberf 22 2021

Tropical Storm Peter Wind Speed FieldTropical Storm Peter – NWS National Hurricane Center Miami FL 1100 PM AST Wed Sep 22, 2021 (see 11:00 video below)

Although a low-level swirl can still be seen in infrared satellite imagery, this feature has continued to lose definition. A recently arriving partial ASCAT-A overpass shows that the circulation has become more elongated, and Peter lacks a well-defined center. In addition, the system has not produced any organized deep convection in quite some time. The cloudiness and convective activity that has been occurring over the western Atlantic has been located along a trough axis well northeast of the decaying circulation center. As a result, Peter no longer meets the definition of a tropical cyclone, and this will be the final NHC advisory on this system. The initial intensity is set at 25 kt in accordance with the ASCAT data. The remnants of Peter are expected to remain within an area of strong upper-level westerly winds, and further weakening should occur over the next day or two. The system has been moving slowly north-northwestward or 335/4 kt. A weakness in the low-level ridge should allow the remnants to turn northward tomorrow, and this general motion should continue through the end of the week.

This is the last NHC advisory on this system.

FORECAST POSITIONS AND MAX WINDS

INIT  23/0300Z 22.1N  67.0W   25 KT  30 MPH - Low (WNW San Juan, PR)
 12H  23/1200Z...DISSIPATED

NWS National Hurricane Center Miami FL 500 PM AST Wed Sep 22, 2021

Peter continues to just barely maintain its classification as a tropical cyclone. While the low-level circulation has remained intact today, the convection continues to be located well downshear to the east. However, there have been a few convective elements forming a bit closer to the center recently and that is the primarily justification for maintaining advisories on Peter as a tropical cyclone this afternoon. The initial intensity is maintained at 30 kt given the earlier scatterometer data, though this might be generous. Continued strong southwesterly vertical wind shear within a dry mid-level environment should ultimately strip the remaining convection away from Peter, with the tropical cyclone expected to finally peter out as a post-tropical remnant low in the next 12 hours.

The depression has been moving very slowly recently, with an estimated north-northwestward motion of 340/4 kt. The cyclone is expected to turn northward and then north-northeastward following a weakness in the low-level ridge until the system finally opens up into a trough, sometime in the 48 to 60 hour period.

FORECAST POSITIONS AND MAX WINDS

INIT  22/2100Z 21.7N  66.7W   30 KT  35 MPH - Depression (ENE San Juan,PR)
 12H  23/0600Z 22.5N  66.8W   25 KT  30 MPH - Post Tropical (WSW Hog Bay,Bermuda)
 24H  23/1800Z 23.5N  66.6W   25 KT  30 MPH - Post Tropical (WSW Hog Bay,Bermuda)
 36H  24/0600Z 24.4N  66.1W   25 KT  30 MPH - Post Tropical (WSW Hog Bay,Bermuda)
 48H  24/1800Z 25.6N  65.3W   25 KT  30 MPH - Post Tropical (WSW Hog Bay,Bermuda)
 60H  25/0600Z...DISSIPATED

NWS National Hurricane Center Miami FL 1100 AM AST Wed Sep 22, 2021 

Peter is barely hanging on to its status as a tropical cyclone this morning. While still closed, the low-level circulation continues to look increasingly diffuse on satellite imagery. In addition, the convective activity, which lacks much organization, remains displaced well to the northeast by moderate to strong southwesterly vertical wind shear. A blend of the latest subjective satellite intensity estimates support keeping Peter as a 30-kt tropical depression this advisory. As has been the story for the last few days, Peter will continue to deal with a lethal combo of 25-35 kt southwesterly vertical wind shear while embedded in a relatively dry mid-level air environment. These factors should ultimately lead to Peter’s demise as a tropical cyclone, with the latest NHC intensity forecast moving the timing up for post-tropical remnant low status to 24 hours. This degeneration could occur as soon as this afternoon if more organized convection does not soon return near the center. Alternatively, Peter may also open up into a trough at any time since the center continues to gradually lose definition.

Similar to prior nights, Peter made another jog to the left after overnight convection diminished near the center. More recently, the depression has begun a slow north-northwestward motion estimated at 330/6 kt. The cyclone is expected to turn northward and then northeastward over the next 24 hours as low-level ridging breaks down south of a deep-layer trough located near Bermuda. The NHC track forecast early on is a bit west of the previous one due to the leftward initial position, but falls in line to a similar track after 24 hours, continuing to split the difference between the GFS and ECMWF models.

As Peter moves poleward away from Puerto Rico, Hispaniola, and the Virgin Islands, the threat of heavy rainfall for these regions associated with the system has diminished.

FORECAST POSITIONS AND MAX WINDS

INIT  22/1500Z 21.6N  66.9W   30 KT  35 MPH - Depression (ENE San Juan,PR)
 12H  23/0000Z 22.3N  67.2W   30 KT  35 MPH - Depression (ENE San Juan,PR)
 24H  23/1200Z 23.3N  67.1W   25 KT  30 MPH - Post Tropical (WSW Hog Bay,Bermuda)
 36H  24/0000Z 24.2N  66.7W   25 KT  30 MPH - Post Tropical (WSW Hog Bay,Bermuda)
 48H  24/1200Z 25.1N  66.3W   25 KT  30 MPH - Post Tropical (WSW Hog Bay,Bermuda)
 60H  25/0000Z 26.3N  65.6W   25 KT  30 MPH - Post Tropical (WSW Hog Bay,Bermuda)
 72H  25/1200Z...DISSIPATED

NWS National Hurricane Center Miami FL 1100 PM AST Tue Sep 21, 2021 

The last visible satellite images of Peter this evening indicated that its low-level center was losing definition and becoming even more elongated. Earlier, new bursts of convection associated with Peter had become oriented along a northeast to southwest axis, a possible sign that Peter may no longer have a well-defined center and could be opening up into a trough. But the estimated center position is now obscured by convective debris, and without recent scatterometer data to prove otherwise, Peter is maintained as a sheared tropical depression for this advisory. The initial intensity of 30 kt is consistent with a UW-CIMSS ADT objective 30-kt estimate and a T2.0/30 kt Dvorak classification from SAB.

It is estimated that Peter is moving northwestward, or 310/6 kt, although this is somewhat uncertain given the degraded low-level structure of the cyclone. The track reasoning remains consistent with previous advisories. Peter is forecast to turn more northward on Wednesday, and then move north-northeastward to northeastward through the end of the week as a trough to the north and northeast of Peter erodes the southern portion of the low-level steering ridge. The track consensus aids have shifted slightly to the right this cycle, and so the latest NHC track forecast has been adjusted a little to the right of the previous one.

Environmental conditions are expected to remain hostile for Peter over the next couple of days. Strong vertical wind shear of 25-30 kt will persist for the next 24-36 h, and GFS and ECMWF model simulated satellite imagery suggest that Peter will be unable to sustain enough deep, organized convection to maintain its status as a tropical cyclone for much longer. Thus, the NHC forecast shows Peter becoming a remnant low in 36 h, with some additional weakening expected before dissipation by this weekend. Of course, without sufficient convection to sustain the low-level vortex, it would not be surprising if the depression degenerated into a trough even sooner than forecast.

Key Messages:

  • 1. Rainfall around the southern periphery of Peter may lead to areas of urban and small stream flooding through early Wednesday across northern Hispaniola, Puerto Rico, and portions of the Virgin Islands.
FORECAST POSITIONS AND MAX WINDS

INIT  22/0300Z 20.8N  65.3W   30 KT  35 MPH - Depression (ENE San Juan,PR)
 12H  22/1200Z 21.6N  66.2W   30 KT  35 MPH - Depression (ENE San Juan,PR)
 24H  23/0000Z 22.6N  66.8W   25 KT  30 MPH - Depression (ENE San Juan,PR)
 36H  23/1200Z 23.6N  66.7W   25 KT  30 MPH - Post Tropical (WSW Hog Bay,Bermuda)
 48H  24/0000Z 24.6N  66.0W   25 KT  30 MPH - Post Tropical (WSW Hog Bay,Bermuda)
 60H  24/1200Z 25.7N  65.1W   25 KT  30 MPH - Post Tropical (WSW Hog Bay,Bermuda)
 72H  25/0000Z...DISSIPATED

NWS National Hurricane Center Miami FL 1100 AM AST Tue Sep 21, 2021 

Like the last several days, this morning’s visible satellite imagery indicates that Peter has become increasingly detached from the remaining fragmented convection that is firing more than 100 n mi east of the center. An Air Force Reserve Reconnaissance aircraft has been sampling the storm this morning and so far has yet to find any flight level (925 mb) or SFMR winds above tropical storm force, although they weren’t able to fly the full pattern in the northeastern quadrant. The initial intensity has been lowered to 35 kt for this advisory, though the data so far suggests this estimate is generous.

After taking a jog to the west overnight, Peter appears to have resumed a slower west-northwest motion at 290/8 kt. Over the next several days, Peter is expected to continue to slow down as it gradually turns to the north and then north-northeast as a deep-layer cyclone to the north is forecast to create a weakness in the current low-level ridging. The track guidance is in general agreement with this scenario, but differences remain in how sharp this rightward turn will be. The latest NHC track forecast has elected to stay close to the track consensus models TVCN and HCCA, and is a bit right of the previous track.

After holding its own against a fairly hostile upper-level wind environment during the last 24-48 hours, Peter appears to finally be succumbing to the combination of 25-30 kt of deep-layer vertical wind shear helping to import sub-50 percent mid-level relative humidity over the center. This shear is not forecast to abate for the next 36-48 hours, and it now appears likely Peter will not be able to survive this unfavorable environment. The latest NHC intensity forecast now weakens Peter to a tropical depression in 12 hours, and degenerates it to a remnant low in 48 hours. However, given the current fragile state of the low-level circulation, it is distinctly possible that Peter may open up into a trough even sooner in the next 24-48 hours.

Key Messages:

  • 1. Rainfall around the southern periphery of Tropical Storm Peter could lead to areas of urban and small stream flooding through today across northern Hispaniola, Puerto Rico, portions of the Virgin Islands, and the Northern Leeward Islands.
FORECAST POSITIONS AND MAX WINDS

INIT  21/1500Z 19.9N  64.7W   35 KT  40 MPH - Tropical Storm (ENE San Juan,PR)
 12H  22/0000Z 20.7N  65.7W   30 KT  35 MPH - Depression (ENE San Juan,PR)
 24H  22/1200Z 21.7N  67.0W   30 KT  35 MPH - Depression (ENE San Juan,PR)
 36H  23/0000Z 22.7N  67.5W   25 KT  30 MPH - Depression (ENE San Salvador,Bahamas)
 48H  23/1200Z 23.4N  67.6W   25 KT  30 MPH - Post Tropical (WSW Hog Bay,Bermuda)
 60H  24/0000Z 24.4N  67.0W   25 KT  30 MPH - Post Tropical (WSW Hog Bay,Bermuda)
 72H  24/1200Z 25.4N  66.2W   25 KT  30 MPH - Post Tropical (WSW Hog Bay,Bermuda)
 96H  25/1200Z 27.5N  64.4W   25 KT  30 MPH - Post Tropical (WSW Hog Bay,Bermuda)
120H  26/1200Z 29.8N  62.5W   25 KT  30 MPH - Post Tropical (WSW Hog Bay,Bermuda)

NWS National Hurricane Center Miami FL 500 PM AST Mon Sep 20, 2021 

Peter’s evolution on satellite today is nearly a repeat of yesterday, with the deep convection having been stripped well east of the center in the morning and then redeveloping over and east of the center by the afternoon. An Air Force Reserve Hurricane Hunter aircraft investigating Peter this morning and early afternoon provided data during a few different passes through the northeast quadrant that supported peak surface winds of 40-45 kt. Since the convection has returned it is reasonable to assume that no weakening has occurred since the aircraft departed the cyclone, and the initial advisory intensity remains 45 kt. Vertical wind shear is forecast to remain near 30 kt for the next few days as Peter interacts with an upper trough to its west, so some weakening is anticipated during that time. By late in the forecast period, the shear should lessen somewhat as the cyclone lifts north of the upper trough. Therefore, slow strengthening is indicated by late this week. There remains a possibility that Peter does not survive the shear over the next few days. However, the storm thus far has shown some resiliency to the hostile environment. The latest NHC intensity forecast is little changed from the previous one and remains near the various intensity consensus solutions.

Peter continues to move west-northwest but at a slightly slower pace of around 12 kt. The forecast track reasoning for the cyclone remains the same. The 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. There were no significant changes to the track or the track guidance from the previous advisory, and the latest NHC track is closest to the TVCN and GFEX consensus tracks.

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  20/2100Z 20.0N  61.8W   45 KT  50 MPH - Tropical Storm (ESE St.John's,A&B)
 12H  21/0600Z 20.6N  63.5W   45 KT  50 MPH - Tropical Storm (ESE St.John's,A&B)
 24H  21/1800Z 21.4N  65.4W   40 KT  45 MPH - Tropical Storm (ENE San Juan,PR)
 36H  22/0600Z 22.2N  66.9W   40 KT  45 MPH - Tropical Storm (ENE San Salvador,Bahamas)
 48H  22/1800Z 23.1N  68.0W   35 KT  40 MPH - Tropical Storm (WSW Hog Bay,Bermuda)
 60H  23/0600Z 24.0N  68.3W   35 KT  40 MPH - Tropical Storm (WSW Hog Bay,Bermuda)
 72H  23/1800Z 25.1N  68.0W   30 KT  35 MPH - Depression (WSW Hog Bay,Bermuda)
 96H  24/1800Z 27.8N  66.9W   30 KT  35 MPH - Depression (WSW Hog Bay,Bermuda)
120H  25/1800Z 30.5N  65.8W   35 KT  40 MPH - Tropical Storm (WSW Hog Bay,Bermuda)

NWS National Hurricane Center Miami FL 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 - Tropical Storm (ESE St.John's,A&B)
 12H  21/0000Z 20.1N  62.7W   40 KT  45 MPH - Tropical Storm (ESE St.John's,A&B)
 24H  21/1200Z 20.8N  64.8W   40 KT  45 MPH - Tropical Storm (WNW Fajardo,PR)
 36H  22/0000Z 21.8N  66.6W   35 KT  40 MPH - Tropical Storm (ENE San Juan,PR)
 48H  22/1200Z 22.7N  67.9W   35 KT  40 MPH - Tropical Storm (ENE San Salvador,Bahamas)
 60H  23/0000Z 23.5N  68.6W   30 KT  35 MPH - Depression (WSW Hog Bay,Bermuda)
 72H  23/1200Z 24.5N  68.7W   30 KT  35 MPH - Depression (WSW Hog Bay,Bermuda)
 96H  24/1200Z 26.5N  67.6W   30 KT  35 MPH - Depression (WSW Hog Bay,Bermuda)
120H  25/1200Z 28.6N  66.4W   35 KT  40 MPH - Tropical Storm (WSW Hog Bay,Bermuda)

NWS National Hurricane Center Miami FL 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 - Tropical Storm (ESE St.John's,A&B)
 12H  20/0600Z 19.1N  59.8W   40 KT  45 MPH - Tropical Storm (ESE St.John's,A&B)
 24H  20/1800Z 19.9N  62.1W   35 KT  40 MPH - Tropical Storm (ESE St.John's,A&B)
 36H  21/0600Z 20.8N  64.3W   35 KT  40 MPH - Tropical Storm (WNW Fajardo,PR)
 48H  21/1800Z 21.9N  66.0W   35 KT  40 MPH - Tropical Storm (ENE San Juan,PR)
 60H  22/0600Z 22.9N  67.2W   35 KT  40 MPH - Tropical Storm (ENE San Salvador,Bahamas)
 72H  22/1800Z 24.1N  68.2W   30 KT  35 MPH - Depression (WSW Hog Bay,Bermuda)
 96H  23/1800Z 26.1N  68.3W   30 KT  35 MPH - Depression (WSW Hog Bay,Bermuda)
120H  24/1800Z 27.7N  67.5W   30 KT  35 MPH - Depression (WSW Hog Bay,Bermuda)

NWS National Hurricane Center Miami FL 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 - Tropical Storm (ESE St.John's,A&B)
 12H  19/1800Z 18.2N  57.0W   40 KT  45 MPH - Tropical Storm (ESE St.John's,A&B)
 24H  20/0600Z 19.3N  58.8W   40 KT  45 MPH - Tropical Storm (ESE St.John's,A&B)
 36H  20/1800Z 20.2N  61.1W   40 KT  45 MPH - Tropical Storm (ENE Philipsburg,SM)
 48H  21/0600Z 21.3N  63.2W   35 KT  40 MPH - Tropical Storm (ESE The Settlement,BVI)
 60H  21/1800Z 22.6N  65.0W   35 KT  40 MPH - Tropical Storm (ENE San Juan,PR)
 72H  22/0600Z 24.3N  65.6W   35 KT  40 MPH - Tropical Storm (ENE San Salvador,Bahamas)
 96H  23/0600Z 25.8N  65.6W   35 KT  40 MPH - Tropical Storm (WSW Hog Bay,Bermuda)
120H  24/0600Z 27.7N  65.2W   35 KT  40 MPH - Tropical Storm (WSW Hog Bay,Bermuda)

NWS National Hurricane Center Miami FL 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 - Depression (ESE St.John's,A&B)
 12H  19/1200Z 17.3N  54.8W   35 KT  40 MPH - Tropical Storm (ESE St.John's,A&B)
 24H  20/0000Z 18.5N  57.3W   40 KT  45 MPH - Tropical Storm (ENE St.John's,A&B)
 36H  20/1200Z 19.4N  59.8W   40 KT  45 MPH - Tropical Storm (ENE St.John's,A&B)
 48H  21/0000Z 20.3N  61.9W   35 KT  40 MPH - Tropical Storm (ENE Philipsburg,SM)
 60H  21/1200Z 21.3N  64.1W   35 KT  40 MPH - Tropical Storm (ESE The Settlement,BVI)
 72H  22/0000Z 22.3N  65.5W   35 KT  40 MPH - Tropical Storm (ENE San Juan,PR)
 96H  23/0000Z 24.4N  66.5W   35 KT  40 MPH - Tropical Storm (ENE San Salvador,Bahamas)
120H  24/0000Z 26.3N  66.2W   35 KT  40 MPH - Tropical Storm (WSW Hog Bay,Bermuda)

NWS National Hurricane Center Miami FL 800 PM EDT Sat Sep 18, 2021

For the North Atlantic…Caribbean Sea and the Gulf of Mexico:

The National Hurricane Center has issued the last advisory on Post-Tropical Cyclone Odette, located a few hundred miles east-southeast of Nantucket, Massachusetts.

  • 1. Showers and thunderstorms associated with an area of low pressure located about 600 miles east-southeast of the northern Leeward Islands continue to show signs of organization. In addition, satellite images and surface observations indicate that the circulation is gradually becoming better defined. If the current trend continues, advisories would likely be initiated on a tropical depression or tropical storm later tonight or early Sunday. This system is expected to be near the northern Leeward Islands on Monday and Tuesday, and interests there should monitor its progress. Upper-level winds are likely to become less conducive for development when the system reaches the southwestern Atlantic by the early to middle part of next week. 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…90 percent. * Formation chance through 5 days…high…90 percent.
  • 2. Showers and thunderstorms are also showing signs of organization in association with a low pressure system located over the far eastern Atlantic a few hundred miles south-southwest of the Cabo Verde Islands. Environmental conditions appear conducive for further development of this system, and a tropical depression is likely to form during the next day or two while moving toward the northwest at 10 to 15 mph to the west of the Cabo Verde Islands. This system is expected to reach cooler waters and an area of stronger upper-level winds early next week, which should limit its development. * Formation chance through 48 hours…high…70 percent. * Formation chance through 5 days…high…70 percent.

NWS National Hurricane Center Miami FL 800 AM EDT Sat Sep 18, 2021

For the North Atlantic…Caribbean Sea and the Gulf of Mexico:

The National Hurricane Center is issuing advisories on Tropical Storm Odette, located a couple of hundred miles south-southeast of Nantucket, Massachusetts.

  • 1. Showers and thunderstorms continue to become better organized in association with an area of low pressure located about 650 miles miles east-southeast of the northern Leeward Islands. Environmental conditions are expected to be conducive for further development during the next day or two, and a tropical depression or tropical storm is expected to form later today or tonight while the system moves toward the west-northwest at about 15 mph. This system is expected to be near the northern Leeward Islands on Monday and Tuesday, and interests there should monitor its progress. Upper-level winds are likely to become less conducive for development when the system reaches the southwestern Atlantic by the early to middle part of next week. 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…90 percent. * Formation chance through 5 days…high…90 percent.
  • 2. A broad area of low pressure is located over the far eastern Atlantic a few hundred miles south of the Cabo Verde Islands. The associated shower and thunderstorm activity has become a little better organized since yesterday, and environmental conditions appear conducive for further development during the next couple of days. A tropical depression could form while the system moves northwestward at about 10 mph to the west of the Cabo Verde Islands before it reaches cooler waters and stronger upper-level winds early next week. * Formation chance through 48 hours…medium…40 percent. * Formation chance through 5 days…medium…40 percent.

NWS National Hurricane Center Miami FL 800 PM EDT Fri Sep 17, 2021

For the North Atlantic…Caribbean Sea and the Gulf of Mexico:

The National Hurricane Center is issuing advisories on newly formed Tropical Storm Odette, located a couple of hundred miles off the Mid-Atlantic U.S. coast. The Weather Prediction Center has issued the last advisory on Post-Tropical Cyclone Nicholas, located over Louisiana.

  • 1. Showers and thunderstorms are gradually becoming better organized in association with an area of low pressure located about 1100 miles east-southeast of the northern Leeward Islands. Environmental conditions are expected to be conducive for further development during the next couple of days, and a tropical depression is likely to form during the next day or two while the system moves toward the west-northwest at about 15 mph. This system is expected to be near the northern Leeward Islands on Monday and Tuesday, and interests there should monitor the progress of this disturbance. Upper-level winds are likely to become less conducive for development when the system reaches the southwestern Atlantic by the early to middle part of next week. * Formation chance through 48 hours…high…80 percent. * Formation chance through 5 days…high…80 percent.
  • 2. A broad area of low pressure located a few hundred miles south of the Cabo Verde Islands continues to produce disorganized showers and thunderstorms. This system is expected to move toward the west and then northwest at 5 to 10 mph over the far eastern Atlantic, and some gradual development is possible over the weekend. However, by early next week, further development appears unlikely as the system is expected to move into strong upper-level winds and over cooler waters. * Formation chance through 48 hours…low…20 percent. * Formation chance through 5 days…low...30 percent.

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Video: Tropics update: Tracking Tropical Depression Peter, Rose