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Tropical Depression Seventeen Forecast Discussion Number 2
2021-09-19 16:54:53| National Hurricane Center (Atlantic)
Issued at 200 PM CVT Sun Sep 19 2021 000 WTNT42 KNHC 191454 TCDAT2 Tropical Depression Seventeen Discussion Number 2 NWS National Hurricane Center Miami FL AL172021 200 PM CVT Sun Sep 19 2021 The low-level center of the depression was exposed on visible satellite imagery this morning but recently a new burst has formed. Since the morning scatterometer passes missed the depression, the intensity is held at 30 kt based on consensus T-2.0 values from TAFB and SAB. The initial motion estimate is 330/12. The cyclone is forecast to move in a general northwestward direction throughout the remainder of the forecast period as the system moves along the southwestern and western periphery of a subtropical ridge that extends westward from Africa across the Cabo Verde Islands. No significant changes were made to the previous NHC forecast track, and the new prediction lies near the middle of the tightly clustered track models. Environmental conditions are conducive for strengthening during the next day or so, with wind shear forecast to drop off later today. Thus, the official forecast calls for strengthening during the next 24 hours, and is close to the lower half of the intensity guidance envelope, near the weaker global models. This forecast could be conservative, since SSTs will be near 27C and mid-level atmospheric moisture will be enough to support intensification. By 36-48 hours, the southwesterly shear will increase, which should end the opportunity for strengthening, and will likely cause slow weakening. The models hold onto this system through the 5 day period, but it is possible that the cyclone could become a remnant low in 4-5 days if the shear is too much for the system to handle. FORECAST POSITIONS AND MAX WINDS INIT 19/1500Z 13.2N 28.8W 30 KT 35 MPH 12H 20/0000Z 14.7N 30.1W 35 KT 40 MPH 24H 20/1200Z 16.7N 32.2W 40 KT 45 MPH 36H 21/0000Z 18.9N 33.9W 40 KT 45 MPH 48H 21/1200Z 21.0N 35.4W 35 KT 40 MPH 60H 22/0000Z 22.7N 36.5W 35 KT 40 MPH 72H 22/1200Z 24.0N 37.6W 35 KT 40 MPH 96H 23/1200Z 26.3N 39.9W 30 KT 35 MPH 120H 24/1200Z 28.3N 41.2W 30 KT 35 MPH $$ Forecaster Hagen/Blake
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Tropical Storm Peter Forecast Discussion Number 3
2021-09-19 14:53:52| National Hurricane Center (Atlantic)
Issued at 900 AM AST Sun Sep 19 2021 000 WTNT41 KNHC 191253 TCDAT1 Tropical Storm Peter Special Discussion Number 3 NWS National Hurricane Center Miami FL AL162021 900 AM AST Sun Sep 19 2021 Satellite imagery as well as data from a Air Force Reserve Hurricane Hunter aircraft indicate that the center of Peter is over 100 n mi west-southwest of its forecast position. Therefore, a special advisory for track is being issued. The forecast track has been adjusted through the first 60 h, resulting in a slight southward adjustment of the track through the first couple of days. The aircraft also measured 925 mb flight-level winds of 56 kt, which supports an initial intensity of 40 kt. No adjustments were made to the intensity forecast. The next full advisory will be issued at 1500 UTC. Based on the track, intensity, and wind radii forecast, no tropical storm watches or warnings are required for the northern Leeward Islands, Virgin Islands or Puerto Rico. However, interests there should monitor the progress of the system as locally heavy rain is possible on Monday and Tuesday when it is expected to pass to the north of the area. Key Messages: 1. Rainfall around the southern periphery of Tropical Storm Peter may lead to areas of urban and small stream flooding from late Sunday into Tuesday across Puerto Rico, the Virgin Islands, and the Northern Leeward Islands. FORECAST POSITIONS AND MAX WINDS INIT 19/1300Z 17.6N 56.0W 40 KT 45 MPH 12H 19/1800Z 18.2N 57.0W 40 KT 45 MPH 24H 20/0600Z 19.3N 58.8W 40 KT 45 MPH 36H 20/1800Z 20.2N 61.1W 40 KT 45 MPH 48H 21/0600Z 21.3N 63.2W 35 KT 40 MPH 60H 21/1800Z 22.6N 65.0W 35 KT 40 MPH 72H 22/0600Z 24.3N 65.6W 35 KT 40 MPH 96H 23/0600Z 25.8N 65.6W 35 KT 40 MPH 120H 24/0600Z 27.7N 65.2W 35 KT 40 MPH $$ Forecaster Latto
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Tropical Depression Seventeen Forecast Discussion Number 1
2021-09-19 10:59:49| National Hurricane Center (Atlantic)
Issued at 800 AM CVT Sun Sep 19 2021 000 WTNT42 KNHC 190859 TCDAT2 Tropical Depression Seventeen Discussion Number 1 NWS National Hurricane Center Miami FL AL172021 800 AM CVT Sun Sep 19 2021 The small low pressure system that the NHC has been tracking the past few days has acquired a well-defined circulation and enough organized deep convection to be classified as a tropical depression. The initial intensity of 30 kt is based on 0000 UTC ASCAT wind data of about 30 kt. This intensity is also supported by consensus Dvorak satellite classifications of T2.0/30 kt from TAFB and SAB. The initial motion estimate is north-northwestward or 330/12 kt. The small cyclone is forecast to move in a general northwestward direction throughout the remainder of the forecast period as the system moves along the southwestern and western periphery of a subtropical ridge that extends westward from Africa across the Cabo Verde Islands. The NHC forecast track lies down the middle of the tightly packed track models. Only modest strengthening is expected during the next 48 hour so while the small cyclone remains over 27-28 deg C sea-surface temperatures and the vertical wind shear decreases to near 5 kt during that time. However, proximity to dry air is expected prevent any significant strengthening from occurring. By late Tuesday, a slow weakening trend is forecast to begin as the system moves over cooler water and the shear increases from the southwest. The NHC intensity forecast closely follows a blend of the IVCN and HCCA intensity consensus models through 72 hours, and then is lower than the HCCA model on days 4 and 5. FORECAST POSITIONS AND MAX WINDS INIT 19/0900Z 11.8N 28.2W 30 KT 35 MPH 12H 19/1800Z 13.4N 29.2W 35 KT 40 MPH 24H 20/0600Z 15.5N 31.2W 40 KT 45 MPH 36H 20/1800Z 17.6N 33.2W 40 KT 45 MPH 48H 21/0600Z 19.7N 34.7W 35 KT 40 MPH 60H 21/1800Z 21.7N 36.1W 35 KT 40 MPH 72H 22/0600Z 23.2N 37.2W 30 KT 35 MPH 96H 23/0600Z 25.6N 39.6W 30 KT 35 MPH 120H 24/0600Z 28.1N 41.5W 30 KT 35 MPH $$ Forecaster Stewart
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Tropical Storm Peter Forecast Discussion Number 2
2021-09-19 10:49:47| National Hurricane Center (Atlantic)
Issued at 500 AM AST Sun Sep 19 2021 389 WTNT41 KNHC 190849 TCDAT1 Tropical Storm Peter Discussion Number 2 NWS National Hurricane Center Miami FL AL162021 500 AM AST Sun Sep 19 2021 Deep convection has increased since the previous advisory, with the convective cloud pattern having taken on a more curved-band configuration compared to the earlier shear pattern. Satellite intensity estimates from TAFB and SAB support increasing the intensity to 35 kt. In addition, earlier ASCAT passes, which missed the center of circulation, did reveal 30-kt winds west of the center in convection-free areas. Thus, it is reasonable to assume that stronger winds are occurring within the deep convection east of the center, which further supports upgrading the system to Tropical Storm Peter with a 35-kt intensity. The initial estimate is an uncertain 305/13 kt. Peter has made a slight jog to the north-northwest since the previous advisory, but this is likely a short-term motion owing to the center redeveloping farther to the north and east into the deep convection. However, a west-northwestward motion is expected to resume later today. Thereafter, the cyclone is forecast to maintain a west-northwestward motion through Wednesday as Peter moves around the southwestern periphery of a strong deep-layer subtropical ridge. On Thursday and Friday, Peter is forecast to turn northward into a weakness in the ridge induced by the large Post-Tropical Cyclone Odette. The new forecast track has been shifted slightly to the right or north of the previous advisory track, mainly due to the more northward initial position, and lies close to the consensus track models TVCA and HCCA. Some strengthening is forecast during the next 24 hours or so as Peter moves over warmer sea-surface temperatures of about 29 deg C. However, proximity to very dry mid-level air and moderate deep-layer southwesterly vertical wind shear are expected to prevent any significant or rapid strengthening. By early Tuesday and beyond, slow weakening is expected to begin due to increasing wind shear. The new official NHC intensity forecast is very similar to the previous advisory, and closely follows a blend of the IVCN and HCCA intensity consensus models. 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 19/0900Z 18.0N 53.5W 35 KT 40 MPH 12H 19/1800Z 18.8N 55.3W 40 KT 45 MPH 24H 20/0600Z 19.8N 57.8W 40 KT 45 MPH 36H 20/1800Z 20.8N 60.1W 40 KT 45 MPH 48H 21/0600Z 21.7N 62.2W 35 KT 40 MPH 60H 21/1800Z 22.7N 63.9W 35 KT 40 MPH 72H 22/0600Z 23.7N 64.9W 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 Stewart
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Tropical Depression Sixteen Forecast Discussion Number 1
2021-09-19 04:31:48| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Sat Sep 18 2021 000 WTNT41 KNHC 190231 TCDAT1 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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