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Tropical Depression Peter Forecast Discussion Number 15

2021-09-22 10:40:30| National Hurricane Center (Atlantic)

Issued at 500 AM AST Wed Sep 22 2021 000 WTNT41 KNHC 220840 TCDAT1 Tropical Depression Peter Discussion Number 15 NWS National Hurricane Center Miami FL AL162021 500 AM AST Wed Sep 22 2021 Peter is a disorganized tropical depression. The low-level center is fully exposed and currently located a couple of hundred miles north of Puerto Rico. Most of the associated thunderstorm activity remains displaced well east of the center due to about 30 kt of westerly shear. The initial intensity is held at 30 kt based on a 0206 UTC ASCAT-B pass that showed a swath of 25-30 kt winds about 60 n mi north of the center. The ASCAT data also showed that the circulation has become quite elongated. Since the hostile conditions of strong westerly shear and dry air entrainment are not expected to let up, a continued gradual decay of Peter is forecast. The system is still predicted to become a remnant low in 36 hours and dissipate in a few days, but both of these could occur sooner. The depression is moving northwestward, with the latest initial motion estimated to be 310/10 kt. The cyclone is expected to turn northward by tonight and then northeastward by the end of the week as the system moves in the flow on the east side of a deep-layer trough. The NHC track forecast is a little to the east of the previous one and close to an average of the GFS and ECMWF models. Key Messages: 1. Rainfall around the southern periphery of Peter may lead to areas of urban and small stream flooding through Thursday morning across northern Hispaniola, Puerto Rico, and portions of the Virgin Islands. FORECAST POSITIONS AND MAX WINDS INIT 22/0900Z 21.5N 66.1W 30 KT 35 MPH 12H 22/1800Z 22.2N 66.7W 30 KT 35 MPH 24H 23/0600Z 23.2N 66.9W 25 KT 30 MPH 36H 23/1800Z 24.1N 66.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 24/0600Z 25.1N 65.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 60H 24/1800Z 26.5N 64.7W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 25/0600Z...DISSIPATED $$ Forecaster Cangialosi

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Tropical Depression Rose Forecast Discussion Number 13

2021-09-22 10:33:24| National Hurricane Center (Atlantic)

Issued at 500 AM AST Wed Sep 22 2021 000 WTNT42 KNHC 220833 TCDAT2 Tropical Depression Rose Discussion Number 13 NWS National Hurricane Center Miami FL AL172021 500 AM AST Wed Sep 22 2021 Rose remains a strongly sheared and poorly organized tropical depression. The low-level center is fully exposed and only a small area of thunderstorms is lingering on the system's east side. The initial intensity is held at 30 kt based on the latest Dvorak estimates. The cyclone is currently in an environment of about 20 kt of northwesterly shear, and dry mid-level air has been entraining into the circulation. Since the shear is expected to increase during the next few days, little change in strength or gradual weakening seems likely. Rose is forecast to become a remnant low by 60 hours when the shear is expected to be near 30 kt, but confidence in the timing of when the system will lose organized convection is low. Some of the models show Rose opening into a trough toward the end of the forecast period, but there are some solutions that hold on to the system for a while longer. The depression is moving northwestward at 7 kt. The system is expected to turn northward in about 36 hours as it moves on the west side of a low- to mid-level ridge. On Friday, a turn to the northeast is expected as Rose gets caught in the flow on the southeast side of a deep-layer trough. The models are in good agreement, and the new NHC track forecast is largely an update of the previous one. FORECAST POSITIONS AND MAX WINDS INIT 22/0900Z 23.4N 38.4W 30 KT 35 MPH 12H 22/1800Z 24.2N 39.4W 30 KT 35 MPH 24H 23/0600Z 25.5N 40.6W 30 KT 35 MPH 36H 23/1800Z 27.0N 41.2W 30 KT 35 MPH 48H 24/0600Z 28.4N 40.6W 30 KT 35 MPH 60H 24/1800Z 29.5N 38.8W 25 KT 30 MPH 72H 25/0600Z 30.1N 36.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 26/0600Z 31.2N 31.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 27/0600Z...DISSIPATED $$ Forecaster Cangialosi

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Tropical Depression Peter Forecast Discussion Number 14

2021-09-22 04:44:18| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Tue Sep 21 2021 000 WTNT41 KNHC 220244 TCDAT1 Tropical Depression Peter Discussion Number 14 NWS National Hurricane Center Miami FL AL162021 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 12H 22/1200Z 21.6N 66.2W 30 KT 35 MPH 24H 23/0000Z 22.6N 66.8W 25 KT 30 MPH 36H 23/1200Z 23.6N 66.7W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 24/0000Z 24.6N 66.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 60H 24/1200Z 25.7N 65.1W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 25/0000Z...DISSIPATED $$ Forecaster Reinhart

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Tropical Depression Rose Forecast Discussion Number 12

2021-09-22 04:38:46| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Tue Sep 21 2021 942 WTNT42 KNHC 220238 TCDAT2 Tropical Depression Rose Discussion Number 12 NWS National Hurricane Center Miami FL AL172021 1100 PM AST Tue Sep 21 2021 Strong northwesterly shear has continued to take a toll on Rose this evening with the remaining deep convection becoming further separated from the low-level center. Unfortunately Rose fell within the gaps of the ASCAT satellite instruments this evening, so there has been no recent scatterometer data. Dvorak T-numbers from TAFB and SAB have continued to decline, and these subjective estimates support lowering Rose's initial intensity to 30 kt. The environment ahead of the cyclone is expected to remain quite hostile with moderate westerly to northwesterly shear and a dry mid-level atmosphere. Simulated satellite imagery from the global models suggest Rose will continue to produce bursts of convection over the eastern portion of its circulation during the next few days which could allow it remain a tropical cyclone during that time. Alternatively, the shear and dry air could cause the system to degenerate into a remnant low much sooner. The latest NHC intensity forecast is similar to the previous advisory and calls for little overall change in strength during the next couple of days, followed by degeneration into a remnant low by day 3. Rose continues to decelerate, now moving northwestward at about 9 kt. The depression should remain on a slow northwestward heading around the western portion of a subtropical ridge during the next 24 to 36 hours. After that time, the cyclone is forecast to turn northward, and then recurve northeastward ahead of a mid- to upper-level trough over the central Atlantic. The dynamical guidance envelope remained fairly steady this cycle and no significant change was made to the previous official forecast. FORECAST POSITIONS AND MAX WINDS INIT 22/0300Z 22.9N 37.9W 30 KT 35 MPH 12H 22/1200Z 23.9N 38.9W 30 KT 35 MPH 24H 23/0000Z 25.0N 40.1W 30 KT 35 MPH 36H 23/1200Z 26.3N 41.0W 30 KT 35 MPH 48H 24/0000Z 27.6N 41.2W 30 KT 35 MPH 60H 24/1200Z 28.9N 40.0W 30 KT 35 MPH 72H 25/0000Z 29.7N 37.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 26/0000Z 31.3N 32.7W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 27/0000Z...DISSIPATED $$ Forecaster Brown

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Tropical Depression Peter Forecast Discussion Number 13

2021-09-21 22:50:48| National Hurricane Center (Atlantic)

Issued at 500 PM AST Tue Sep 21 2021 000 WTNT41 KNHC 212050 TCDAT1 Tropical Depression Peter Discussion Number 13 NWS National Hurricane Center Miami FL AL162021 500 PM AST Tue Sep 21 2021 Like clockwork compared to prior days, deep convection has reignited closer to the increasingly elongated low-level circulation of Peter. Despite this increase in convective coverage, there does not appear to be much if any organization to this activity, with the upper-level cirrus taking on the appearance of a shapeless blob. In addition, an earlier 1157 UTC ASCAT-A pass received just after the prior advisory showed a peak wind retrieval of only 29 kt, well to the north of the low-level circulation. Furthermore, NOAA buoy 41043, located north of the center of Peter, has been observing peak 1-minute sustained winds between 20-25 kt over the last 6 hours. These lower winds, in combination with the lack of tropical storm force winds observed by the earlier Air Force Reserve Reconnaissance mission provide enough justification to downgrade Peter to a tropical depression this advisory with maximum sustained winds of 30 kt. The ongoing afternoon convection appears to have slowed down the forward motion of Peter a bit this afternoon, but the heading remains off to the west-northwest at 300/7 kt. Peter is still expected to gradually move to the west-northwest in the short term, followed by a somewhat sharp turn to the north and north-northeast as a weakness in the low-level flow develops from a deep-layer trough positioned near Bermuda. Similar to this morning, the guidance is in general agreement on this solution, with some cross- and along-track spread. The latest NHC track forecast is just a bit more right compared to the previous advisory, leaning a bit closer to the consensus aids which have also shifted a bit right this advisory. Peter's convective activity is unlikely to help improve the increasingly elongated vortex, mainly because the convection is likely to entrain dry mid-level air that often results in cool downdrafts disrupting the low-level cyclonic circulation more than helping. With deep-layer shear between 25-35 kt expected to persist for the next 36 hours in both the GFS- and ECMWF-SHIPS guidance, gradual weakening is likely to continue. By 36 hours, while intermittent bursts of deep convection will remain possible over warm sea-surface temperatures, both the GFS and ECMWF forecast simulated IR brightness temperatures show the convection becoming increasingly disorganized and unlikely to sustain Peter's status as a tropical cyclone. Thus, the cyclone is now forecast to become a remnant low in 36 hours. However, given that Peter's circulation is becoming increasingly elongated, it is also possible the system may open up into a trough even before this time period. Key Messages: 1. Rainfall around the southern periphery of Tropical Depression Peter could lead to areas of urban and small stream flooding through the evening across northern Hispaniola, Puerto Rico, portions of the Virgin Islands, and the Northern Leeward Islands. FORECAST POSITIONS AND MAX WINDS INIT 21/2100Z 20.5N 65.0W 30 KT 35 MPH 12H 22/0600Z 21.3N 66.1W 30 KT 35 MPH 24H 22/1800Z 22.3N 67.2W 25 KT 30 MPH 36H 23/0600Z 23.2N 67.4W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 23/1800Z 24.2N 66.9W 25 KT 30 MPH...POST-TROP/REMNT LOW 60H 24/0600Z 25.3N 66.1W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 24/1800Z 26.7N 65.1W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 25/1800Z 28.7N 63.7W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 26/1800Z...DISSIPATED $$ Forecaster Papin

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