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Tropical Storm Karen Forecast Discussion Number 14

2019-09-25 16:50:52| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Wed Sep 25 2019 000 WTNT42 KNHC 251450 TCDAT2 Tropical Storm Karen Discussion Number 14 NWS National Hurricane Center Miami FL AL122019 1100 AM AST Wed Sep 25 2019 Karen is still having a tough time establishing and maintaining a well-organized structure. The deep convection which developed over the center earlier this morning has since collapsed, leaving a ragged and disorganized cloud pattern. In addition, a sizable outflow boundary moving away from the eastern part of the circulation suggests that there is dry air within the vortex. The initial intensity is being held at 40 kt, pending possible scatterometer data later this morning and a reconnaissance flight this afternoon. The initial position is a little difficult to locate, but the best estimate of the current motion is 360/13 kt. Karen is moving northward between a mid-level high centered over the central Atlantic and a mid- to upper-level low located just east of the Bahamas. This low is expected to slowly retrograde westward, with ridging developing over the western Atlantic by day 3. This change in steering will cause Karen to turn northeastward during the next 48 hours but then make a clockwise loop once it is blocked by the ridge. After day 3, the ridge should force Karen to move west-southwestward. Most of the track models agree on this general scenario. There is some latitudinal spread on days 4 and 5 after the loop occurs, with the HWRF being the most notable outlier by not showing much of a westward motion. The consensus aids, however, have remained fairly steady, and therefore there was no compelling reason to make any significant changes compared to the previous track forecast. Except for the possibility of dry air in the circulation, it's not quite evident why Karen has not been able to sustain organization. Still, the cyclone is expected to move beneath an upper-level anticyclone during the next 24-48 hours, and if the shear does indeed decrease, then some strengthening would be expected. There continues to be a dichotomy among the intensity models, with the dynamical models (including the GFS and ECMWF) keeping the cyclone weak while the statistical-dynamical models still show intensification through days 4 and 5. It's difficult to ignore what's being shown by the global models, since there must be something in the environment that they're deeming to be negative for continued strengthening. The best course of action at this point is to maintain a steady intensity after 48 hours, but it should be noted that what is shown in the official forecast still lies above the ICON intensity consensus and the HCCA corrected consensus aid. Key Messages: 1. Karen will continue to produce heavy rainfall, potentially causing additional flash floods and mudslides, across Puerto Rico and the Virgin Islands today even as the center moves away from the region. FORECAST POSITIONS AND MAX WINDS INIT 25/1500Z 21.7N 64.9W 40 KT 45 MPH 12H 26/0000Z 23.4N 64.4W 45 KT 50 MPH 24H 26/1200Z 25.4N 63.7W 45 KT 50 MPH 36H 27/0000Z 26.9N 62.9W 50 KT 60 MPH 48H 27/1200Z 27.5N 62.0W 55 KT 65 MPH 72H 28/1200Z 26.8N 62.0W 55 KT 65 MPH 96H 29/1200Z 26.0N 65.0W 55 KT 65 MPH 120H 30/1200Z 25.5N 68.5W 55 KT 65 MPH $$ Forecaster Berg

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Hurricane Lorenzo Forecast Discussion Number 11

2019-09-25 16:36:24| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Wed Sep 25 2019 000 WTNT43 KNHC 251436 TCDAT3 Hurricane Lorenzo Discussion Number 11 NWS National Hurricane Center Miami FL AL132019 1100 AM AST Wed Sep 25 2019 Conventional satellite imagery indicates that Lorenzo continues to become better organized, with a small central convective feature surrounded by a large complex of outer bands in all quadrants except the northwest, where some dry air may be entraining. Satellite intensity estimates from TAFB, SAB, and the CIMMS satellite consensus technique have increased to near 75 kt, and that will be the initial intensity for this advisory. The hurricane currently has good cirrus outflow in all directions. The initial motion is 285/15. The subtropical ridge to the north and northeast of Lorenzo should steer the hurricane west- northwestward for the next day or so, followed by a turn toward the northwest as a break develops in the ridge between 45W-50W. Lorenzo is subsequently forecast to turn northward into the break by 96 h and recurve into the westerlies around 120 h. While the guidance agrees with this scenario, there is some spread on the longitude of the recurvature between the easternmost GFS model and the westernmost ECMWF model. The new forecast lies between these models in best overall agreement with the HCCA corrected consensus guidance. Lorenzo should remain over warm water and in a light shear environment during the next three days, with the only negative factor for intensification being episodic intrusions of dry air. The intensity guidance forecasts continued steady strengthening, with rapid strengthening possible during the first 24-36 h. The new intensity forecast is increased from the previous forecast, and for the first 36-48 h it lies near the upper edge of the intensity guidance. The intensity forecast shows little change in strength between 36-72 h, although some fluctuations in intensity are likely due to eyewall replacement cycles during this time. After 72 h, Lorenzo is likely to encounter some southwesterly shear, and thus some weakening is forecast. FORECAST POSITIONS AND MAX WINDS INIT 25/1500Z 14.1N 35.1W 75 KT 85 MPH 12H 26/0000Z 14.4N 37.1W 85 KT 100 MPH 24H 26/1200Z 15.3N 39.2W 100 KT 115 MPH 36H 27/0000Z 16.7N 40.8W 110 KT 125 MPH 48H 27/1200Z 18.4N 42.2W 110 KT 125 MPH 72H 28/1200Z 21.9N 44.2W 110 KT 125 MPH 96H 29/1200Z 25.0N 44.5W 105 KT 120 MPH 120H 30/1200Z 29.0N 42.0W 105 KT 120 MPH $$ Forecaster Beven

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Hurricane Lorenzo Forecast Discussion Number 10

2019-09-25 10:57:18| National Hurricane Center (Atlantic)

Issued at 500 AM AST Wed Sep 25 2019 000 WTNT43 KNHC 250857 TCDAT3 Hurricane Lorenzo Discussion Number 10 NWS National Hurricane Center Miami FL AL132019 500 AM AST Wed Sep 25 2019 Deep convection has continued to increase in coverage and intensity near the center of Lorenzo during the past several hours. There have been no good microwave passes over the cyclone since yesterday, however, a partial SSMIS pass showed hints that a mid-level eye is forming. The initial intensity has been increased to 70 kt based on a blend of the latest subjective Dvorak estimates from TAFB and SAB, and objective estimates from the UW-CIMSS ADT and SATCON. Lorenzo is the 5th hurricane of the Atlantic hurricane season. The SHIPS and DTOPS rapid intensification probability models both show that there is a greater than 50 percent chance that Lorenzo will strengthen by 25 kt or more during the next 24 hours. The large size of the cyclone appears to be the only obvious inhibiting factor to rapid intensification since the environment is otherwise quite favorable for continued strengthening. The NHC forecast now shows Lorenzo becoming a major hurricane in 36 hours, faster than previously anticipated. By 72 h and beyond, most of the guidance keeps Lorenzo in a nearly steady state. In reality, most strong hurricanes have some short-term fluctuations in intensity, but such fluctuations are nearly impossible to forecast this far out in time. Regardless of its exact intensity, confidence is high that Lorenzo will be a large and powerful hurricane over the eastern and central Atlantic through the rest of this week. No changes of significance were made to the track forecast. Lorenzo is still forecast to move west-northwestward for the next day or so, before turning northwestward toward a weakness in the subtropical ridge. A turn toward the north is anticipated by the end of the forecast period. The models are still in fairly good agreement on the track of the hurricane, and the NHC forecast is between the consensus aids HCCA and TVCA. FORECAST POSITIONS AND MAX WINDS INIT 25/0900Z 13.6N 33.9W 70 KT 80 MPH 12H 25/1800Z 14.0N 36.0W 85 KT 100 MPH 24H 26/0600Z 14.7N 38.4W 95 KT 110 MPH 36H 26/1800Z 15.9N 40.2W 100 KT 115 MPH 48H 27/0600Z 17.5N 41.6W 105 KT 120 MPH 72H 28/0600Z 21.1N 44.3W 105 KT 120 MPH 96H 29/0600Z 24.0N 45.0W 105 KT 120 MPH 120H 30/0600Z 27.4N 43.5W 105 KT 120 MPH $$ Forecaster Zelinsky/Ramos

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Post-Tropical Cyclone Jerry Forecast Discussion Number 32

2019-09-25 10:54:20| National Hurricane Center (Atlantic)

Issued at 500 AM AST Wed Sep 25 2019 000 WTNT45 KNHC 250854 TCDAT5 Post-Tropical Cyclone Jerry Discussion Number 32 NWS National Hurricane Center Miami FL AL102019 500 AM AST Wed Sep 25 2019 Jerry has lacked organized deep convection since around 1500 UTC yesterday. It is therefore now designated as a post-tropical cyclone. However, a Tropical Storm Warning remains in effect for Bermuda, and advisories will continue to be issued on Jerry until it no longer poses any threat to the island. An Air Force Reserve Hurricane Hunter aircraft continued to fly through Jerry after the last advisory. The plane reported that Jerry's wind field has become quite asymmetric, with no tropical-storm-force winds in the western half of the cyclone. That said, on its last pass through the southeast quadrant of the cyclone the plane reported max flight level winds of 55 kt at 925 mb and believable SFMR winds of 40 kt. The intensity of Jerry is therefore maintained at 40 kt for this advisory. With no deep convection to sustain it, the cyclone should gradually spin down during the next few days. The dynamical models indicate that Jerry will dissipate in about 4 days and the NHC forecast does as well. A mid-latitude trough to the north has caused Jerry to turn northeastward, and the initial motion estimate is 055/6 kt. The models are in good agreement that the post-tropical low will continue generally northeastward today and tomorrow, steered by low-level southwesterly flow. On this track, the cyclone will pass very near Bermuda later today. The models are in excellent agreement on the track of Jerry, and only small adjustments were made to the previous NHC track forecast. Key Messages: 1. Tropical-storm-force winds are expected on Bermuda later today. Large swells are also expected to affect the coast of Bermuda during the next few days. These swells could cause life-threatening rip currents. See products issued by the Bermuda Weather Service for more information. FORECAST POSITIONS AND MAX WINDS INIT 25/0900Z 31.8N 67.9W 40 KT 45 MPH...POST-TROPICAL 12H 25/1800Z 32.3N 66.5W 35 KT 40 MPH...POST-TROPICAL 24H 26/0600Z 33.0N 64.2W 35 KT 40 MPH...POST-TROPICAL 36H 26/1800Z 33.9N 61.7W 30 KT 35 MPH...POST-TROP/REMNT LOW 48H 27/0600Z 34.6N 59.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 28/0600Z 34.0N 55.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 29/0600Z...DISSIPATED $$ Forecaster Zelinsky

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Tropical Storm Karen Forecast Discussion Number 13

2019-09-25 10:52:51| National Hurricane Center (Atlantic)

Issued at 500 AM AST Wed Sep 25 2019 000 WTNT42 KNHC 250852 TCDAT2 Tropical Storm Karen Discussion Number 13 NWS National Hurricane Center Miami FL AL122019 500 AM AST Wed Sep 25 2019 Karen's convection has increased significantly and become better organized since the previous advisory. The well-defined low-level circulation center that previously had been fully exposed now has intense convection with cloud tops of -85C to -90C almost completely encircling the center at times. During the last leg of an earlier Air Force Reserve reconnaissance mission, an 850-mb flight-level wind of 46 kt and SFMR surface winds of 37 kt were observed in the southeastern quadrant, suggesting that Karen may have weakened slightly during an earlier convective hiatus. However, the recent increase in deep convection over the center, along with a pronounced increase in the Doppler velocities and the development of a smaller radius of maximum winds of less than 10 nmi above 20,000 ft, suggest that Karen has likely strengthened. For now, however, the intensity is being maintained at 40 kt. The secondary mid-level circulation that had developed north of Puerto Rico several hours ago has since weakened based on San Juan Doppler radar data and satellite images. Now that deep convection has redeveloped, resulting in a stronger and deeper the vortex column, the motion has steadied off in a northerly direction of 360/12 kt over the past 6 hours. A northward motion is forecast to continue this morning, followed by a turn toward the north-northeast by this afternoon. A north-northeastward to northeastward motion accompanied by a gradual decrease in forward speed is expected in the 12-48 hour period. By 72 hours, steering currents are forecast to collapse and Karen is expected to stall or make a clockwise loop. By 96 and beyond, the global models forecast that a ridge will build eastward from the southeastern United States to Bermuda, forcing Karen in a slow westward to west-southwestward direction. The new NHC track forecast is very close to the previous advisory track, and lies close to the simple consensus track model TVCN, which is about midway between the corrected-consensus models FSSE located to the north and NOAA-HCCA to the south. The intensity forecast remains somewhat perplexing with the dynamical global and regional models showing no strengthening for the next 4 days, followed by weakening and even dissipation by day 5, whereas the GFS- and ECMWF-based statistical-dynamical models show slow but steady strengthening during the forecast period with Karen becoming a hurricane by 120 hours. The main reasons for global models weakening the cyclone is due to the low- and upper-level circulations decoupling in about 3 days, followed by very dry mid-level overspreading of the low-level circulation, shutting off convective development. The problem with that scenario is that Karen will be moving into very low vertical shear conditions and underneath an upper-level anticyclone by 36 hours, which favors strengthening since the cyclone will also be sitting over 29 deg C water of considerable depth. For now, the new official intensity forecast remains a compromise between the weak dynamical model solutions and the stronger SHIPS intensity forecasts, which is a little above the intensity consensus models IVCN, HCCA, and FSSE. Key Messages: 1. Karen will continue to produce rainfall causing flash floods and mudslides across Puerto Rico, Vieques and the U.S. and British Virgin Islands today even as the center moves away from the region. FORECAST POSITIONS AND MAX WINDS INIT 25/0900Z 20.5N 65.2W 40 KT 45 MPH 12H 25/1800Z 22.3N 64.5W 45 KT 50 MPH 24H 26/0600Z 24.5N 63.9W 45 KT 50 MPH 36H 26/1800Z 26.4N 63.2W 50 KT 60 MPH 48H 27/0600Z 27.3N 62.5W 55 KT 65 MPH 72H 28/0600Z 27.1N 61.9W 55 KT 65 MPH 96H 29/0600Z 26.3N 64.4W 55 KT 65 MPH 120H 30/0600Z 25.9N 67.8W 55 KT 65 MPH $$ Forecaster Stewart

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