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Tropical Storm Kirk Forecast Discussion Number 2

2018-09-22 22:38:56| National Hurricane Center (Atlantic)

Issued at 500 PM AST Sat Sep 22 2018 925 WTNT42 KNHC 222038 TCDAT2 Tropical Storm Kirk Discussion Number 2 NWS National Hurricane Center Miami FL AL122018 500 PM AST Sat Sep 22 2018 The convection associated with Kirk is currently disorganized, with the majority of it in a cluster to the west of the center. Most of the subjective and objective satellite intensity estimates are in the 30-35 kt range, so the initial intensity remains 35 kt for this advisory. The forecast track takes Kirk over SSTs around 27C for the next 36 h or so with generally low shear, which appears favorable for gradual strengthening. However, there is a possibility that entrainment of dry air from an area of African dust present to the north of Kirk may allow less intensification than currently forecast. From 36-72 h, there is some divergence in the intensity guidance between the SHIPS and LGEM models, which forecast strengthening into a hurricane, and the dynamical models, which forecast little additional strengthening. The intensity forecast leans toward the dynamical models during that period. After 72 h, Kirk should encounter increasing westerly shear and gradually weaken. The intensity forecast, which is unchanged from the previous forecast, lies a little above the intensity consensus IVCN. The initial motion is now 290/13. The subtropical ridge to the north of the storm should steer Kirk quickly westward for the next 72 h or so, with forward speeds reaching 20-25 kt. Later in the forecast period, Kirk should turn west-northwestward with a decrease in forward speed as it nears a developing weakness in the ridge near and to the east of the Lesser Antilles. The new forecast track, which is closest to the HCCA consensus model, is shifted a little to the north of the previous track. However, it continues to lie on the south side of the guidance envelope. FORECAST POSITIONS AND MAX WINDS INIT 22/2100Z 8.6N 24.8W 35 KT 40 MPH 12H 23/0600Z 9.1N 27.1W 40 KT 45 MPH 24H 23/1800Z 9.5N 31.2W 45 KT 50 MPH 36H 24/0600Z 9.7N 35.7W 50 KT 60 MPH 48H 24/1800Z 9.8N 40.2W 50 KT 60 MPH 72H 25/1800Z 10.5N 48.0W 50 KT 60 MPH 96H 26/1800Z 11.5N 54.0W 45 KT 50 MPH 120H 27/1800Z 13.0N 59.0W 40 KT 45 MPH $$ Forecaster Beven

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Tropical Depression Eleven Forecast Discussion Number 4

2018-09-22 22:37:26| National Hurricane Center (Atlantic)

Issued at 500 PM AST Sat Sep 22 2018 490 WTNT41 KNHC 222037 TCDAT1 Tropical Depression Eleven Discussion Number 4 NWS National Hurricane Center Miami FL AL112018 500 PM AST Sat Sep 22 2018 Since the last advisory was issued, deep convection decreased in association with the depression to the point that it was not classifiable with the Dvorak technique at 18Z. However, there are a couple of patches of thunderstorms that have developed recently, and if they persist they could help the system hold on to tropical cyclone status a bit longer. The low-level center remains exposed with UW-CIMSS now analyzing nearly 45 kt of westerly shear over the cyclone. Gradual spin down is expected during the next 12 to 24 hours, and the cyclone should become a remnant low by Sunday. Global model fields show the surface circulation dissipating by 36 hours and that is indicated in the official forecast. The low-level center has been moving erratically today, with a recent northward jog seen, but the long-term initial motion estimate is 305/03. The weakening cyclone should be steered west- northwestward by a weak low-level ridge through dissipation, and the NHC track forecast has been nudged northward toward the latest multi-model consensus. FORECAST POSITIONS AND MAX WINDS INIT 22/2100Z 13.6N 53.9W 25 KT 30 MPH 12H 23/0600Z 13.9N 54.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 24H 23/1800Z 14.4N 56.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 36H 24/0600Z...DISSIPATED $$ Forecaster Brennan

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Tropical Storm Kirk Forecast Discussion Number 1

2018-09-22 16:36:53| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Sat Sep 22 2018 310 WTNT42 KNHC 221436 TCDAT2 Tropical Storm Kirk Discussion Number 1 NWS National Hurricane Center Miami FL AL122018 1100 AM AST Sat Sep 22 2018 The area of low pressure located well south of the Cabo Verde Islands now has a well-defined center and enough organized deep convection to be considered a tropical cyclone. The initial intensity is set to 35 kt based on data from recent ASCAT passes that showed an area of 30-35 kt winds northwest of the center. Kirk will be moving over SSTs around 27C for the next 36 hours or so with generally low shear, which should allow for some gradual strengthening. After that time, the SSTs increase quickly along the forecast track, but the SHIPS model and global model fields show the vertical shear increasing, in part due to the very fast low-level easterly flow. In addition, the GFS and ECMWF global models don't show much development of the cyclone during the forecast period. As a result of these factors, little change in strength is forecast after 48 hours. The NHC forecast is close to the HCCA consensus aid through 48 hours and is near IVCN afterward. The initial motion estimate is 280/12, but has the usual uncertainty for a system in the early stages of development. The cyclone is expected to be steered very quickly westward at low latitudes with forward speeds reaching 20-25 kt over the next 72 hours to the south of a mid-level ridge. Late in the period, some gain in latitude and a slight decrease in forward speed are shown as a weakness in the ridge develops to the east of the Lesser Antilles. The initial NHC track forecast is close to HCCA and a little south of the TVCA consensus, giving a little more weight to the GFS and ECMWF, which lie on the south side of the track guidance envelope. FORECAST POSITIONS AND MAX WINDS INIT 22/1500Z 8.3N 23.6W 35 KT 40 MPH 12H 23/0000Z 8.8N 25.7W 40 KT 45 MPH 24H 23/1200Z 9.3N 29.6W 45 KT 50 MPH 36H 24/0000Z 9.4N 34.0W 50 KT 60 MPH 48H 24/1200Z 9.6N 38.6W 50 KT 60 MPH 72H 25/1200Z 10.3N 46.8W 50 KT 60 MPH 96H 26/1200Z 11.0N 53.0W 50 KT 60 MPH 120H 27/1200Z 12.5N 58.5W 45 KT 50 MPH $$ Forecaster Brennan

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Tropical Depression Eleven Forecast Discussion Number 3

2018-09-22 16:32:26| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Sat Sep 22 2018 345 WTNT41 KNHC 221432 TCDAT1 Tropical Depression Eleven Discussion Number 3 NWS National Hurricane Center Miami FL AL112018 1100 AM AST Sat Sep 22 2018 It appears that the depression's best day is behind it, as the cloud pattern has become less organized this morning. The low-level center is becoming increasingly separated from the warming cloud tops in what remains of the deep convection, which is displaced to the east by nearly 40 kt of west-southwesterly shear as analyzed by UW-CIMSS. The initial intensity has been lowered to 25 kt, consistent with a T1.0 classification from TAFB. Given that the strong shear is expected to continue and the depression will be moving through a relatively dry environment, the cyclone should gradually spin down and become a remnant low by 24 hours and dissipate by 48 hours. However, I would not be surprised if either or both of these occurred sooner. The center of the depression hasn't moved much during the past few hours, but a long-term initial motion estimate is 280/03. The weakening cyclone should be steered westward to west-northwestward by a low-level ridge. The new NHC track forecast is north of the previous one but remains along the southern edge of the guidance envelope given doubts about how much latitude such a shallow system will gain prior to dissipation. FORECAST POSITIONS AND MAX WINDS INIT 22/1500Z 13.2N 53.8W 25 KT 30 MPH 12H 23/0000Z 13.6N 54.5W 25 KT 30 MPH 24H 23/1200Z 14.0N 55.7W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 24/0000Z 14.4N 56.8W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 24/1200Z...DISSIPATED $$ Forecaster Brennan

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Tropical Depression Eleven Forecast Discussion Number 2

2018-09-22 10:36:22| National Hurricane Center (Atlantic)

Issued at 500 AM AST Sat Sep 22 2018 624 WTNT41 KNHC 220836 TCDAT1 Tropical Depression Eleven Discussion Number 2 NWS National Hurricane Center Miami FL AL112018 500 AM AST Sat Sep 22 2018 Deep convection remains displaced to the east of the depression's center due to 30-40 kt of westerly shear. Although Dvorak final-T numbers from TAFB and SAB have decreased since yesterday--now a consensus T1.0--the initial intensity is held, perhaps generously, at 30 kt. Strong westerly shear is expected to persist for several days, which at the very least will prevent the depression from getting any better organized. Since the global models show the depression opening up into a trough in about 24 hours, the new NHC intensity forecast brings down the winds a little faster, shows the system becoming a remnant low by 36 hours, and dissipates the low entirely by 48 hours well east of the Windward Islands. This evolution could certainly occur more quickly than indicated by the official forecast. The center of the depression has not been moving much, and it's possible the sheared convection is trying to pull it back toward the east. However, the average motion over the past 12 hours is westward, or 270/4 kt. The track guidance insists that the depression should move slowly west-northwestward over the next couple of days, but given that the system has not made any northward progress, I elected to skirt the southern edge of the guidance envelope. This new forecast is a little south of the previous NHC track prediction. FORECAST POSITIONS AND MAX WINDS INIT 22/0900Z 13.0N 53.5W 30 KT 35 MPH 12H 22/1800Z 13.3N 54.3W 30 KT 35 MPH 24H 23/0600Z 13.6N 55.4W 25 KT 30 MPH 36H 23/1800Z 13.8N 56.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 24/0600Z...DISSIPATED $$ Forecaster Berg

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