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Hurricane Norman Forecast Discussion Number 8

2018-08-30 10:47:04| National Hurricane Center (East Pacific)

Issued at 200 AM PDT Thu Aug 30 2018 291 WTPZ41 KNHC 300846 TCDEP1 Hurricane Norman Discussion Number 8 NWS National Hurricane Center Miami FL EP162018 200 AM PDT Thu Aug 30 2018 Norman is in the midst of a remarkable period of rapid intensification. An eye developed in infrared satellite imagery around 0500 UTC and is completely surrounded by very cold cloud tops quadrants. A burst of lightning also began a couple of hours ago in the southeastern quadrant, where cloud tops are as cold as -84C. Subjective Dvorak estimates rose quickly to T5.5/102 kt from SAB and T5.0/90 kt from TAFB at 0600 UTC, and since the satellite presentation has continued to improve, the initial intensity is set near the top of that range at 100 kt, making Norman a major hurricane. Norman's intensity has increased by an estimated 45-50 kt over the past 24 hours. Norman remains in a low-shear environment with good upper-level outflow in all quadrants, and the hurricane is moving over very warm waters of 29-30 degrees Celsius. Barring any unforeseen structural changes like an eyewall replacement, Norman is likely to continue strengthening for the next 24 hours or so, and nearly all of the intensity models depict the current rapid intensification phase persisting for the next 12 hours. The updated NHC intensity forecast has been increased during the first 48 hours to account for recent trends, and it closely matches an average of the HCCA model, Florida State Superensemble, and ICON intensity consensus. A very gradual weakening is expected after 48 hours as Norman encounters some shear and cooler waters. A strong subtropical ridge extending west of northern Mexico is steering Norman westward, or 275/6 kt. The depth and strength of the ridge is expected to force Norman west-southwestward during the next 24-48 hours, followed by a turn back toward the west and then west-northwest on days 3-5. The track models are in fairly good agreement throughout the 5-day forecast period, although there are some differences in exactly how much of an S-curve Norman will make. The ECMWF shows the most pronounced bend in the forecast track, starting along the southern periphery of the guidance envelope and then moving to the northern periphery by days 4 and 5. Although the new NHC track forecast does not follow the ECMWF exactly, it does show slightly more bend than the previous forecast. FORECAST POSITIONS AND MAX WINDS INIT 30/0900Z 17.8N 117.4W 100 KT 115 MPH 12H 30/1800Z 17.9N 118.5W 115 KT 130 MPH 24H 31/0600Z 17.6N 120.1W 120 KT 140 MPH 36H 31/1800Z 17.0N 121.6W 120 KT 140 MPH 48H 01/0600Z 16.3N 123.3W 115 KT 130 MPH 72H 02/0600Z 16.2N 127.1W 105 KT 120 MPH 96H 03/0600Z 18.0N 132.0W 95 KT 110 MPH 120H 04/0600Z 20.0N 137.5W 75 KT 85 MPH $$ Forecaster Berg

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Hurricane Norman Forecast Discussion Number 7

2018-08-30 04:37:00| National Hurricane Center (East Pacific)

Issued at 800 PM PDT Wed Aug 29 2018 848 WTPZ41 KNHC 300236 TCDEP1 Hurricane Norman Discussion Number 7 NWS National Hurricane Center Miami FL EP162018 800 PM PDT Wed Aug 29 2018 Norman is steadily strengthening. Recent microwave images indicate that the hurricane now has a well-defined inner core with a banded eye feature evident in that data. The eye is not yet apparent in geostationary images, but the convective pattern is improving in organization and the cloud tops continue to become colder. A blend of the satellite intensity estimates at 0000 UTC supported an initial intensity of 70 kt, and since the system continues to become better organized, the initial wind speed for this advisory is increased to 75 kt. Now that Norman has an inner core, rapid intensification is expected during the next 24 hours or so while the hurricane remains in near ideal environmental conditions. The SHIPS rapid intensification indices are very high, and the NHC intensity forecast remains near the upper end of the model guidance in the short term. Beyond a couple of days, an increase in shear and slightly cooler waters should promote a gradual weakening trend. Satellite images suggest that the forward speed of Norman has slowed to 280/7 kt. All of the models show a mid-level ridge amplifying to the north of the tropical cyclone during the next few days, and this should cause the hurricane to move westward or west-southwestward during that time. Thereafter, a turn back to the west and then west-northwest with an increase in forward speed is predicted as Norman moves closer to the western periphery of the ridge. The model guidance remains in fairly good agreement, and the NHC track forecast lies near the various consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 30/0300Z 17.9N 116.5W 75 KT 85 MPH 12H 30/1200Z 18.0N 117.6W 95 KT 110 MPH 24H 31/0000Z 18.0N 119.2W 105 KT 120 MPH 36H 31/1200Z 17.5N 120.8W 115 KT 130 MPH 48H 01/0000Z 16.8N 122.5W 110 KT 125 MPH 72H 02/0000Z 16.0N 126.3W 105 KT 120 MPH 96H 03/0000Z 16.9N 130.9W 95 KT 110 MPH 120H 04/0000Z 18.5N 136.0W 80 KT 90 MPH $$ Forecaster Cangialosi

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Hurricane Miriam Forecast Discussion Number 15

2018-08-29 23:49:01| National Hurricane Center (East Pacific)

Issued at 200 PM PDT Wed Aug 29 2018 673 WTPZ45 KNHC 292148 CCA TCDEP5 Hurricane Miriam Discussion Number 15...Corrected NWS National Hurricane Center Miami FL EP152018 200 PM PDT Wed Aug 29 2018 Corrected WMO header in fourth paragraph The satellite presentation of Miriam has significantly improved over the past 12 hours or so. Several microwave images received since the release of the previous advisory revealed a significant increase in organization with convection wrapping nearly completely around the center. Recent visible satellite images have shown hints of an eye, but the surrounding convective tops have warmed somewhat. Subjective and objective Dvorak intensity estimates all support hurricane strength, and the initial intensity is increased to 65 kt for this advisory. Satellite fixes show that Miriam has slowed down and is moving westward or 270/8 kt. The hurricane is near the western edge of the subtropical ridge and is forecast to turn west-northwestward very soon. A large mid- to upper-level trough located northeast of the Hawaiian Islands should cause Miriam to turn northwestward, then northward over the next couple of days, and the dynamical models are in good agreement through 72 hours. After that time, model differences remain as the ECMWF continues to take a deeper cyclone much faster northward than the remainder of the guidance. The NHC forecast continues to lean toward the solution of a weaker cyclone turning northwestward or west-northwestward near the end of the forecast period. The updated NHC forecast is once again south of the model consensus at days 4 and 5 and is in best agreement with the GFS ensemble mean. Miriam has about another 12-24 h over warm water and within a light to moderate wind shear environment in which to strengthen. After that time, a significant increase in southwesterly shear is anticipated and Miriam is forecast to weaken fairly quickly between 36 and 72 hours. Miriam should reach SSTs below 26C by 96 h and should degenerate into a remnant low by that time. Miriam will move into the Central Pacific Basin shortly and this is last NHC advisory on this system. Future information on Miriam can be found in advisories issued by the Central Pacific Hurricane Center beginning at 5 PM HST (0300 UTC), under AWIPS header HFOTCPCP3, WMO header WTPA33 PHFO, and on the web at http://www.prh.noaa.gov/cphc FORECAST POSITIONS AND MAX WINDS INIT 29/2100Z 14.0N 139.7W 65 KT 75 MPH 12H 30/0600Z 14.4N 140.7W 70 KT 80 MPH 24H 30/1800Z 15.3N 141.3W 75 KT 85 MPH 36H 31/0600Z 16.7N 141.5W 70 KT 80 MPH 48H 31/1800Z 18.4N 141.5W 60 KT 70 MPH 72H 01/1800Z 21.5N 142.7W 40 KT 45 MPH 96H 02/1800Z 24.7N 145.5W 30 KT 35 MPH...POST-TROP/REMNT LOW 120H 03/1800Z 27.0N 149.5W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Brown

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Hurricane Norman Forecast Discussion Number 6

2018-08-29 22:44:28| National Hurricane Center (East Pacific)

Issued at 200 PM PDT Wed Aug 29 2018 894 WTPZ41 KNHC 292044 TCDEP1 Hurricane Norman Discussion Number 6 NWS National Hurricane Center Miami FL EP162018 200 PM PDT Wed Aug 29 2018 Norman's cloud pattern has continued to organize with numerous convective bands and excellent upper-level outflow. More importantly, satellite images show an eye feature which has been depicted intermittently. Dvorak numbers from TAFB and SAB have reached T4.0, and on this basis, Norman is being upgraded to hurricane status in this advisory. The environment of low shear and warm ocean continues to be ideal for intensification, and guidance continues to be pretty aggressive in bringing the winds up fast. The NHC forecast indicates rapid intensification, and predicts Norman to become a major hurricane in about 24 hours. Norman appears to be moving toward the west or 270 degrees at 8 kt. The high pressure ridge which is controlling the motion of the hurricane is expanding westward, and the flow pattern around the ridge should steer Norman on a west or even west-southwest track for the next 3 to 4 days. Track guidance continues to be in remarkably good agreement, and models are tightly clustered at least for the next 3 to 4 days. The NHC forecast is very similar to the previous one, and continue to lie very close to the corrected consensus HCCA and the multi-model aids. The confidence in the track forecast is quite high at this time. FORECAST POSITIONS AND MAX WINDS INIT 29/2100Z 17.6N 116.1W 65 KT 75 MPH 12H 30/0600Z 17.8N 117.3W 80 KT 90 MPH 24H 30/1800Z 17.9N 118.8W 100 KT 115 MPH 36H 31/0600Z 17.5N 120.5W 110 KT 125 MPH 48H 31/1800Z 17.0N 122.0W 115 KT 130 MPH 72H 01/1800Z 16.0N 125.5W 110 KT 125 MPH 96H 02/1800Z 16.0N 130.0W 100 KT 115 MPH 120H 03/1800Z 17.5N 135.0W 90 KT 105 MPH $$ Forecaster Avila

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Hurricane Miriam Forecast Discussion Number 15

2018-08-29 22:44:28| National Hurricane Center (East Pacific)

Issued at 200 PM PDT Wed Aug 29 2018 895 WTPZ45 KNHC 292044 TCDEP5 Hurricane Miriam Discussion Number 15 NWS National Hurricane Center Miami FL EP152018 200 PM PDT Wed Aug 29 2018 The satellite presentation of Miriam has significantly improved over the past 12 hours or so. Several microwave images received since the release of the previous advisory revealed a significant increase in organization with convection wrapping nearly completely around the center. Recent visible satellite images have shown hints of an eye, but the surrounding convective tops have warmed somewhat. Subjective and objective Dvorak intensity estimates all support hurricane strength, and the initial intensity is increased to 65 kt for this advisory. Satellite fixes show that Miriam has slowed down and is moving westward or 270/8 kt. The hurricane is near the western edge of the subtropical ridge and is forecast to turn west-northwestward very soon. A large mid- to upper-level trough located northeast of the Hawaiian Islands should cause Miriam to turn northwestward, then northward over the next couple of days, and the dynamical models are in good agreement through 72 hours. After that time, model differences remain as the ECMWF continues to take a deeper cyclone much faster northward than the remainder of the guidance. The NHC forecast continues to lean toward the solution of a weaker cyclone turning northwestward or west-northwestward near the end of the forecast period. The updated NHC forecast is once again south of the model consensus at days 4 and 5 and is in best agreement with the GFS ensemble mean. Miriam has about another 12-24 h over warm water and within a light to moderate wind shear environment in which to strengthen. After that time, a significant increase in southwesterly shear is anticipated and Miriam is forecast to weaken fairly quickly between 36 and 72 hours. Miriam should reach SSTs below 26C by 96 h and should degenerate into a remnant low by that time. Miriam will move into the Central Pacific Basin shortly and this is last NHC advisory on this system. Future information on Miriam can be found in advisories issued by the Central Pacific Hurricane Center beginning at 5 PM HST (0300 UTC), under AWIPS header HFOTCPCP3, WMO header WTPA32 PHFO, and on the web at http://www.prh.noaa.gov/cphc FORECAST POSITIONS AND MAX WINDS INIT 29/2100Z 14.0N 139.7W 65 KT 75 MPH 12H 30/0600Z 14.4N 140.7W 70 KT 80 MPH 24H 30/1800Z 15.3N 141.3W 75 KT 85 MPH 36H 31/0600Z 16.7N 141.5W 70 KT 80 MPH 48H 31/1800Z 18.4N 141.5W 60 KT 70 MPH 72H 01/1800Z 21.5N 142.7W 40 KT 45 MPH 96H 02/1800Z 24.7N 145.5W 30 KT 35 MPH...POST-TROP/REMNT LOW 120H 03/1800Z 27.0N 149.5W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Brown

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