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Hurricane Norman Forecast Discussion Number 23

2018-09-02 22:34:19| National Hurricane Center (East Pacific)

Issued at 200 PM PDT Sun Sep 02 2018 670 WTPZ41 KNHC 022034 TCDEP1 Hurricane Norman Discussion Number 23 NWS National Hurricane Center Miami FL EP162018 200 PM PDT Sun Sep 02 2018 Norman has maintained a very distinct eye with a ring of deep convection all day. T-numbers from both TAFB and SAB have not changed and still are T6.0 on the Dvorak scale. On this basis, the initial intensity is being kept at 115 kt in this advisory. The hurricane, however, will begin to approach lower SSTs, and intensity guidance is responding to the cooler water by gradually weakening the hurricane. The NHC forecast continues to follow the intensity consensus IVCN, and forecasts a gradual weakening beyond 12 hours. Norman is moving toward the west-northwest at 16 kt. There is a strong subtropical ridge anchored to the north of the hurricane, and this flow pattern will continue to steer the cyclone between the west and west-northwest at the same speed for the next 2 days or so. After that time, Norman will be near the southwestern edge of the ridge, and a turn toward the northwest should then begin. Most of the guidance shifted northward at very long ranges, so the NHC forecast was slightly adjusted in that direction accordingly. FORECAST POSITIONS AND MAX WINDS INIT 02/2100Z 18.1N 130.9W 115 KT 130 MPH 12H 03/0600Z 18.7N 133.5W 115 KT 130 MPH 24H 03/1800Z 19.5N 136.7W 100 KT 115 MPH 36H 04/0600Z 20.0N 140.0W 85 KT 100 MPH 48H 04/1800Z 20.5N 142.7W 80 KT 90 MPH 72H 05/1800Z 21.0N 147.0W 70 KT 80 MPH 96H 06/1800Z 23.0N 150.0W 60 KT 70 MPH 120H 07/1800Z 26.0N 152.5W 45 KT 50 MPH $$ Forecaster Avila

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Tropical Storm Florence Forecast Discussion Number 13

2018-09-02 16:49:17| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Sun Sep 02 2018 647 WTNT41 KNHC 021449 TCDAT1 Tropical Storm Florence Discussion Number 13 NWS National Hurricane Center Miami FL AL062018 1100 AM AST Sun Sep 02 2018 Florence's convective cloud appearance has become rather disheveled this morning, with most of the deep convection sheared to the east and northeast of the now fully exposed but well-defined low-level circulation center. Both subjective and objective satellite intensity estimates have decreased, especially the objective ADT estimates from UW-CIMSS. Based on a blend of the available estimates, the intensity has been lowered to 45 kt. The initial motion is 285/16. Now that the system has weakened and become more vertically shallow, a more westward component of motion is expected throughout the forecast period. All but the GFS and HWRF models have picked up on this more westerly component of motion, and the ECMWF and UKMET models are now the southernmost models in the guidance suite. Since the ridge to the north is expected to remain intact and even build more westward over the next 5 days, the new NHC track forecast has been shifted southward and to the left of the previous advisory track, and lies close to a blend of the HCCA, FSSE, and TCVN track consensus models. Analyses from UW-CIMSS indicate that westerly to southwesterly vertical wind shear of 15-20 kt is undercutting the otherwise favorable upper-level outflow pattern noted in water vapor imagery and by the GFS- and ECMWF-based SHIPS model, which show the shear to be less than 10 kt. GOES-16 mid-level water vapor imagery also reveals that Florence is ingesting considerable dry air in the western and southern quadrants, with the dry mid-level air having penetrated into the inner-core region. Since the vertical shear is expected to get a little worse over the next 3-4 days while the cyclone is moving over SSTs near 26 deg C, little change in strength is forecast through 96 h. By 120 h, however, Florence is forecast to move over warmer waters with SSTs exceeding 28 deg C and also into a weaker shear environment, which should allow for some re-strengthening to occur. The new NHC intensity forecast is a little lower than the one in the previous advisory, and closely follows the consensus model IVCN, through 96 h, and then is a little above the guidance at 120 h. FORECAST POSITIONS AND MAX WINDS INIT 02/1500Z 17.0N 33.2W 45 KT 50 MPH 12H 03/0000Z 17.4N 35.3W 45 KT 50 MPH 24H 03/1200Z 17.9N 38.2W 45 KT 50 MPH 36H 04/0000Z 18.4N 40.7W 45 KT 50 MPH 48H 04/1200Z 18.9N 42.8W 45 KT 50 MPH 72H 05/1200Z 20.5N 47.0W 45 KT 50 MPH 96H 06/1200Z 22.4N 51.0W 45 KT 50 MPH 120H 07/1200Z 24.3N 54.3W 55 KT 65 MPH $$ Forecaster Stewart

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Hurricane Norman Forecast Discussion Number 22

2018-09-02 16:38:16| National Hurricane Center (East Pacific)

Issued at 800 AM PDT Sun Sep 02 2018 561 WTPZ41 KNHC 021438 TCDEP1 Hurricane Norman Discussion Number 22 NWS National Hurricane Center Miami FL EP162018 800 AM PDT Sun Sep 02 2018 Norman has made a remarkable and surprising come back today. Satellite images reveal a distinct eye surrounded by a ring of very deep convection, and Dvorak T-numbers from both TAFB and SAB reached T6.0 around 1200 UTC. These numbers have leveled off since then. On this basis, the initial intensity has been increased to 115 kt, making Norman again a Category Four Hurricane on the Saffir-Simpson Scale. The hurricane, however, will begin to approach lower SSTs, and although some of the intensity models are more aggressive in forecasting strengthening, the NHC forecast prefers the consensus IVCN, and forecasts a gradual weakening beyond 12 to 24 hours. Norman is moving toward the west-northwest at 16 kt. There is a strong subtropical ridge anchored to the north of Norman, and this flow pattern will continue to steer the hurricane between the west and west-northwest at the same speed for the next 2 to 3 days. By then, the ridge is forecast to be weaker and a turn toward the northwest is expected by the end of the forecast period. Track guidance is in very good agreement, and unanimously, all models forecast the gradual turn to the northwest beyond 4 days. The NHC track forecast is in the middle of the envelope and is not much different from the earlier one. FORECAST POSITIONS AND MAX WINDS INIT 02/1500Z 17.6N 129.1W 115 KT 130 MPH 12H 03/0000Z 18.2N 131.5W 115 KT 130 MPH 24H 03/1200Z 19.1N 134.7W 100 KT 115 MPH 36H 04/0000Z 20.0N 138.2W 90 KT 105 MPH 48H 04/1200Z 20.5N 141.5W 80 KT 90 MPH 72H 05/1200Z 21.0N 146.0W 70 KT 80 MPH 96H 06/1200Z 22.0N 150.0W 65 KT 75 MPH 120H 07/1200Z 24.0N 153.0W 55 KT 65 MPH $$ Forecaster Avila

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Tropical Storm Olivia Forecast Discussion Number 7

2018-09-02 16:36:46| Tropical Depression LIDIA

Issued at 900 AM MDT Sun Sep 02 2018

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Hurricane Norman Forecast Discussion Number 21

2018-09-02 10:53:15| National Hurricane Center (East Pacific)

Issued at 200 AM PDT Sun Sep 02 2018 498 WTPZ41 KNHC 020853 TCDEP1 Hurricane Norman Discussion Number 21 NWS National Hurricane Center Miami FL EP162018 200 AM PDT Sun Sep 02 2018 Norman's structure has continued to slowly improve this morning. A ragged, but fairly clear, eye has been apparent in shortwave and longwave IR imagery for the past several hours, and cloud tops around the eye have generally cooled. The initial intensity has been held at 90 kt, in agreement with the latest Dvorak fixes from TAFB and SAB. However, the most recent objective intensity estimates from the UW-CIMSS ADT are slightly higher, suggesting this estimate could be conservative. Given that Norman appears to be on the upswing, the forecast now allows for some slight re-strengthening over the next 12 h while the hurricane remains over warm waters and the shear is expected to be light. Beyond that time, however, there has been no significant change to the intensity forecast reasoning or the guidance. The cyclone is still expected to gradually weaken as it encounters a marginal environment consisting of cool SSTs, fairly dry air, and by the end of the forecast period, increasing shear. At 24 h and beyond, the NHC forecast is very close to the intensity consensus, and has not been substantially changed from the previous advisory. Norman is beginning to accelerate and the initial motion estimate is 290/11. A strong deep-layer subtropical ridge to the north should keep Norman moving generally westward to west-northwestward through most of the forecast period, with a notable increase in speed for the next day or two. All of the models agree on this general scenario, however there is still some north-south spread in the guidance, with the GFS and ECMWF on opposite sides of the guidance envelope. Like the previous forecast, the official track forecast generally splits these models and lies near the middle of the guidance envelope and the consensus aids, FSSE and HCCA. FORECAST POSITIONS AND MAX WINDS INIT 02/0900Z 17.1N 127.5W 90 KT 105 MPH 12H 02/1800Z 17.7N 129.8W 95 KT 110 MPH 24H 03/0600Z 18.6N 133.0W 90 KT 105 MPH 36H 03/1800Z 19.4N 136.3W 85 KT 100 MPH 48H 04/0600Z 20.1N 139.7W 80 KT 90 MPH 72H 05/0600Z 20.8N 144.6W 70 KT 80 MPH 96H 06/0600Z 21.5N 149.0W 65 KT 75 MPH 120H 07/0600Z 23.0N 152.0W 60 KT 70 MPH $$ Forecaster Zelinsky

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