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Tropical Depression Peter Forecast Discussion Number 17
2021-09-22 22:58:08| National Hurricane Center (Atlantic)
Issued at 500 PM AST Wed Sep 22 2021 000 WTNT41 KNHC 222058 TCDAT1 Tropical Depression Peter Discussion Number 17 NWS National Hurricane Center Miami FL AL162021 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 12H 23/0600Z 22.5N 66.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 24H 23/1800Z 23.5N 66.6W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 24/0600Z 24.4N 66.1W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 24/1800Z 25.6N 65.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 60H 25/0600Z...DISSIPATED $$ Forecaster Papin
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Tropical Depression Eighteen Forecast Discussion Number 1
2021-09-22 22:54:37| National Hurricane Center (Atlantic)
Issued at 500 PM AST Wed Sep 22 2021 000 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
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Tropical Depression Rose Forecast Discussion Number 15
2021-09-22 22:37:39| National Hurricane Center (Atlantic)
Issued at 500 PM AST Wed Sep 22 2021 000 WTNT42 KNHC 222037 TCDAT2 Tropical Depression Rose Discussion Number 15 NWS National Hurricane Center Miami FL AL172021 500 PM AST Wed Sep 22 2021 Rose is currently comprised of a swirl of low-level clouds, with the only significant convection occurring about 120 n mi southeast of the center. Satellite intensity estimates have decreased, and are now 25 kt from TAFB and too weak to classify from SAB. Based mainly on earlier scatterometer data, the initial intensity is held at a possibly generous 30 kt. Rose remain in an area of northwesterly shear and upper-level convergence, and dry mid-level air has been entraining into the circulation. The large-scale model guidance indicates that the hostile conditions will continue for at least another 36 h, and based on model forecasts of convection Rose is now expected to degenerate into a remnant low pressure area in 24 h or less. It should be noted that the GFS and HWRF models suggest the possibility that convection could re-develop in the 48-96 h period due to the remnant low interacting with an upper-level trough. For now, the intensity forecast will not call for re-generation at that time. The initial motion is now west-northwestward or 300/9 kt. A northwestward motion is expected for the next 12-24 hours as Rose or its remnants are steered by a mid-level ridge over the eastern Atlantic. After that time, the system is expected to turn northward, northeastward, and eventually east-northeastward as it becomes steered by a deep-layer trough that includes the remnants of Odette. Since Rose has moved a bit to the west of the previous forecast, the guidance and the new forecast track have also shifted westward during the first 36 h. The new NHC track is to the east of the consensus models for the first 36 h, and close to the consensus aids after that time. FORECAST POSITIONS AND MAX WINDS INIT 22/2100Z 24.2N 40.2W 30 KT 35 MPH 12H 23/0600Z 25.2N 41.3W 30 KT 35 MPH 24H 23/1800Z 26.7N 41.7W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 24/0600Z 28.0N 41.4W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 24/1800Z 29.0N 39.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 60H 25/0600Z 29.5N 36.9W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 25/1800Z 30.1N 34.1W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 26/1800Z 31.9N 30.4W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 27/1800Z...DISSIPATED $$ Forecaster Beven
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Tropical Depression Peter Forecast Discussion Number 16
2021-09-22 16:53:34| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Wed Sep 22 2021 000 WTNT41 KNHC 221453 TCDAT1 Tropical Depression Peter Discussion Number 16 NWS National Hurricane Center Miami FL AL162021 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 12H 23/0000Z 22.3N 67.2W 30 KT 35 MPH 24H 23/1200Z 23.3N 67.1W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 24/0000Z 24.2N 66.7W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 24/1200Z 25.1N 66.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 60H 25/0000Z 26.3N 65.6W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 25/1200Z...DISSIPATED $$ Forecaster Papin
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Tropical Depression Rose Forecast Discussion Number 14
2021-09-22 16:39:09| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Wed Sep 22 2021 000 WTNT42 KNHC 221438 TCDAT2 Tropical Depression Rose Discussion Number 14 NWS National Hurricane Center Miami FL AL172021 1100 AM AST Wed Sep 22 2021 Rose is currently comprised of a swirl of low-level clouds with no significant convection, with an earlier burst dissipating during the last few hours. Recently received scatterometer data show 25-30 kt winds in the northeastern quadrant, so the initial intensity is held at 30 kt. The cyclone remains in an environment of northwesterly shear and upper-level convergence, and dry mid-level air has been entraining into the circulation. Since the shear is expected to increase during the next 2-3 days, the cyclone is expected to gradually weaken during this time. However, confidence in the timing of when the system will stop producing organized convection is still low. The new intensity forecast calls for Rose to degenerate into a remnant low between 60-72 h, but it is possible this could happen earlier. The initial motion is now 305/8 kt. The depression is expected to turn northward in 24-36 hours as it moves on the west side of a low- to mid-level ridge over the eastern Atlantic. By 48-60 h, a turn to the northeast is expected as Rose gets caught in the flow on the southeast side of a deep-layer trough over the north Atlantic. Based on the initial position and motion, the first 36 h of the forecast track are shifted a little to the west of the previous track. After that time, the new forecast track is similar to the previous track. FORECAST POSITIONS AND MAX WINDS INIT 22/1500Z 23.6N 39.2W 30 KT 35 MPH 12H 23/0000Z 24.6N 40.1W 30 KT 35 MPH 24H 23/1200Z 26.1N 41.1W 30 KT 35 MPH 36H 24/0000Z 27.6N 41.1W 30 KT 35 MPH 48H 24/1200Z 28.8N 39.9W 25 KT 30 MPH 60H 25/0000Z 29.4N 37.8W 25 KT 30 MPH 72H 25/1200Z 29.9N 34.9W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 26/1200Z 31.5N 30.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 27/1200Z...DISSIPATED $$ Forecaster Beven
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