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Hurricane Ophelia Forecast Discussion Number 16

2017-10-13 04:50:21| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Thu Oct 12 2017 000 WTNT42 KNHC 130250 TCDAT2 Hurricane Ophelia Discussion Number 16 NWS National Hurricane Center Miami FL AL172017 1100 PM AST Thu Oct 12 2017 Remarkably, the hurricane has continued to strengthen this evening. Satellite images indicate that cloud tops in the eyewall have cooled in the past several hours, with a warm eye remaining. Dvorak estimates from TAFB, SAB and CIMSS range between 90 to 95 kt, so the initial intensity is raised to 90 kt. It seems that the marginal SSTs that Ophelia has been moving over have been offset by the cold upper-level temperatures and low shear environment. SSTs only slightly cool in the next 24 hours with similar shear conditions, so a minor decrease in strength is in the forecast. After that time, while the hurricane should move over colder waters, it will likely be accelerating to the northeast and experiencing favorable mid-latitude jet dynamics, which will help to maintain the cyclone's intensity. All of the guidance show extratropical transition by 3 days with the cyclone keeping hurricane-force winds, as indicated in the new forecast. Little change was made to the previous prediction, except to account for the higher initial wind speed. Ophelia is finally moving, estimated at 6 kt to the east-northeast. This general motion with an increase in forward speed is expected for the next couple of days as the hurricane gets picked up by a large mid-latitude trough. Confidence in the track forecast remains fairly high for the first 72 h, although the spread increases after that time. The GFS-based guidance generally then show a more northward track to the west of Ireland then over the far North Atlantic, while the UKMET/ECMWF show a track over Ireland and Great Britain then eastward and dissipating over northern Europe. The forecast is close to the consensus at long range, but some large changes could be required for later forecasts. While the NHC track keeps the center of Ophelia south and east of the Azores, tropical-storm-force winds are possible throughout the Azores by Saturday night due to an approaching front. In addition, the wind field of Ophelia will likely expand as the cyclone begins extratropical transition, and any deviation to the left of the forecast track could bring stronger winds to the islands. Interests in the Azores should refer to products issued by the Azores Weather Forecast and Watch Center. KEY MESSAGES: 1. Ophelia is expected to transition to a hurricane-force post- tropical cyclone by Monday when it moves near Ireland and the United Kingdom. While post-tropical Ophelia will likely bring some direct impacts from wind and heavy rain to portions of these areas, as well as dangerous marine conditions, given the forecast uncertainty at these time ranges it is too soon to determine the exact magnitude, timing and location of the impacts. Residents in Ireland and the United Kingdom should monitor the progress of Ophelia for the next several days. For more information on local impacts, residents of Ireland should refer to products issued by Met Eireann and residents in the United Kingdom should refer to products issued by the Met Office. FORECAST POSITIONS AND MAX WINDS INIT 13/0300Z 30.7N 34.7W 90 KT 105 MPH 12H 13/1200Z 31.2N 33.5W 90 KT 105 MPH 24H 14/0000Z 32.2N 31.1W 85 KT 100 MPH 36H 14/1200Z 33.7N 27.5W 80 KT 90 MPH 48H 15/0000Z 36.0N 23.0W 80 KT 90 MPH 72H 16/0000Z 45.0N 14.5W 75 KT 85 MPH...POST-TROP/EXTRATROP 96H 17/0000Z 56.0N 7.0W 55 KT 65 MPH...POST-TROP/EXTRATROP 120H 18/0000Z 64.0N 0.5W 50 KT 60 MPH...POST-TROP/EXTRATROP $$ Forecaster Blake

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Hurricane Ophelia Forecast Discussion Number 15

2017-10-12 22:37:45| National Hurricane Center (Atlantic)

Issued at 500 PM AST Thu Oct 12 2017 000 WTNT42 KNHC 122037 TCDAT2 Hurricane Ophelia Discussion Number 15 NWS National Hurricane Center Miami FL AL172017 500 PM AST Thu Oct 12 2017 Ophelia's structure has continued to improve during the afternoon. The eye of the hurricane has cleared and is surrounded by a ring of cloud tops colder than -55 deg C. Dvorak classifications from TAFB and the UW-CIMSS ADT have increased accordingly, and on that basis the initial intensity has been increased to 85 kt. Ophelia is nearly stationary, which could cause the hurricane to stop strengthening, or even weaken slightly during the next 12 to 24 hours due to upwelling effects. That said, the intensity guidance is in good agreement that Ophelia will remain at hurricane strength for the next 48 h while it remains in a fairly unstable, low-shear environment. Beyond that time, extratropical transition will begin, though baroclinic forcing will likely keep post-tropical Ophelia near hurricane strength as it approaches Ireland and the UK. The new intensity forecast is very similar to the previous advisory, and is generally close to the multi-model intensity consensus. Although Ophelia is currently stationary, a mid-latitude trough should cause it to begin moving toward the east-northeast within about 24 hours. The cyclone will then accelerate on that heading in the faster mid-latitude westerly flow ahead of the trough, before turning toward the northeast around day 3 as extratropical transition occurs and the hurricane becomes entangled with the southern extent of the trough. Confidence in the track forecast is fairly high for the first 72 h, and all of the dynamical guidance is tightly clustered through this period. The model spread increases substantially at 96 h and beyond. As a post-tropical cyclone, Ophelia will continue to interact with the southern extent of the trough, and should turn toward the northeast as a result of this interaction. However, the details of this turn vary greatly from model to model. The new NHC forecast has been nudged slightly toward the east at this time range, closer to the UKMET and ECMWF models, as well as the corrected consensus aids HCCA and FSSE. While the track guidance keeps the center of Ophelia south and east of the Azores, tropical-storm-force winds are possible throughout the Azores by Sunday due to an approaching front. In addition, the wind field of Ophelia will likely expand as the cyclone begins extratropical transition, and any deviation to the left of the forecast track could bring stronger winds to the islands. Interests in the Azores should refer to products issued by the Azores Weather Forecast and Watch Center. KEY MESSAGES: 1. Ophelia is expected to transition to a hurricane-force post- tropical cyclone by Monday when it moves near Ireland and the United Kingdom. While post-tropical Ophelia will likely bring some direct impacts from wind and heavy rain to portions of these areas, as well as dangerous marine conditions, given the forecast uncertainty at these time ranges it is too soon to determine the exact magnitude, timing and location of the impacts. Residents in Ireland and the United Kingdom should monitor the progress of Ophelia for the next several days. For more information on local impacts, residents of Ireland should refer to products issued by Met Eireann and residents in the United Kingdom should refer to products issued by the Met Office. FORECAST POSITIONS AND MAX WINDS INIT 12/2100Z 30.4N 35.5W 85 KT 100 MPH 12H 13/0600Z 31.0N 34.6W 85 KT 100 MPH 24H 13/1800Z 31.9N 32.6W 80 KT 90 MPH 36H 14/0600Z 33.2N 29.6W 75 KT 85 MPH 48H 14/1800Z 35.0N 25.6W 75 KT 85 MPH 72H 15/1800Z 42.6N 17.1W 75 KT 85 MPH 96H 16/1800Z 53.0N 10.0W 65 KT 75 MPH...POST-TROP/EXTRATROP 120H 17/1800Z 62.5N 2.0W 55 KT 65 MPH...POST-TROP/EXTRATROP $$ Forecaster Zelinsky

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Hurricane Ophelia Forecast Discussion Number 13

2017-10-12 10:40:19| National Hurricane Center (Atlantic)

Issued at 500 AM AST Thu Oct 12 2017 000 WTNT42 KNHC 120840 TCDAT2 Hurricane Ophelia Discussion Number 13 NWS National Hurricane Center Miami FL AL172017 500 AM AST Thu Oct 12 2017 Satellite imagery indicates that Ophelia continues to gradually become better organized, with the hurricane maintaining a well-defined eye and the cloud tops in the eyewall gradually cooling. The various subjective and objective satellite intensity estimates range between 75-90 kt, and based on the previous trend of the intensity being near the lower end of the estimates, the initial intensity is kept at a possibly conservative 75 kt. The initial motion is 040/3. Ophelia is currently in an area of light steering currents to the south of the mid-latitude westerlies. The large-scale models forecast a deep-layer trough to amplify over the central and northeastern Atlantic during the forecast period, which should steer Ophelia northeastward or east-northeastward at an increasing forward speed for the next few days. The track guidance has changed little since the last advisory, and the new forecast track, which leans toward the HFIP Corrected Consensus and the Florida State Superensemble, is an update of the previous forecast. Ophelia is forecast to remain in a light to moderate shear environment and over marginal sea surface temperatures for the next 24-36 h, and the intensity forecast shows some strengthening during this time in agreement with the guidance. After that, the hurricane is expected to move over cooler water. As that happens, though, interaction with the above-mentioned westerly trough should help Ophelia keep its intensity. Extratropical transition should begin by 72 h, with Ophelia likely to become a hurricane-force baroclinic low by 96 h. The guidance is in good agreement that Ophelia should affect Ireland, northern Ireland and Great Britain between 96-120 h as a powerful extratropical low. Although the track guidance keeps the center offshore of the Azores, a tropical storm watch or warning could be needed for the eastern Azores on Thursday because of the forecasted increase in wind radii in the northwestern quadrant of the cyclone. FORECAST POSITIONS AND MAX WINDS INIT 12/0900Z 30.3N 35.6W 75 KT 85 MPH 12H 12/1800Z 30.7N 35.2W 80 KT 90 MPH 24H 13/0600Z 31.3N 34.0W 80 KT 90 MPH 36H 13/1800Z 32.2N 32.0W 75 KT 85 MPH 48H 14/0600Z 33.7N 28.6W 75 KT 85 MPH 72H 15/0600Z 38.5N 20.5W 75 KT 85 MPH 96H 16/0600Z 49.0N 13.5W 70 KT 80 MPH...POST-TROP/EXTRATROP 120H 17/0600Z 59.0N 7.0W 55 KT 65 MPH...POST-TROP/EXTRATROP $$ Forecaster Beven

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Hurricane Ophelia Forecast Discussion Number 11

2017-10-11 22:31:34| National Hurricane Center (Atlantic)

Issued at 500 PM AST Wed Oct 11 2017 000 WTNT42 KNHC 112031 TCDAT2 Hurricane Ophelia Discussion Number 11 NWS National Hurricane Center Miami FL AL172017 500 PM AST Wed Oct 11 2017 Intensity estimates for Ophelia still range wildly. Dvorak estimates, both subjective and objective, continue to support a much higher intensity than other satellite-derived maximum wind estimates. Adding to the uncertainty, subjective Dvorak classifications at 1800 UTC were higher than 6 hours prior, but since that time, the ragged eye has become obscured in IR imagery. However, a recent SSMIS pass at 1813 UTC indicated that the convective structure of the cyclone has improved during the day, so it wouldn't be surprising if the eye became apparent again shortly. In an attempt to blend all available data, the initial intensity has been increased to 65 kt, making Ophelia a hurricane. However, it should be stressed that the uncertainty of the initial intensity is higher than normal. The hurricane is moving slowly toward the east and the initial motion estimate is 090/3 kt. The hurricane is embedded within weak steering flow, and only a slow northeastward drift is expected for the next 24 h. After that time, an approaching deep-layer trough should force Ophelia to accelerate toward the northeast. All of the deterministic models are in fairly good agreement on the speed and track of Ophelia, however the various model ensembles suggest that the uncertainty is much higher, especially regarding the forward speed of Ophelia beyond 48 h. The official track forecast favors the deterministic model solutions, in part to maintain continuity with the previous advisory. The track forecast is therefore close to the multi-model consensus, but much faster than the various ensemble mean aids. Since it isn't clear exactly how strong Ophelia is, the intensity forecast is low confidence. All of the intensity guidance indicates that strengthening is likely for the next 24 to 36 hours, however the near stationary motion of the hurricane could induce some upwelling and limit the extent to which the hurricane may strengthen. Around 72 hours, the shear should begin to increase substantially as Ophelia begins to interact with the approaching trough, and extratropical transition will likely begin, accompanied by a broadening of the wind field and a gradual decrease of the maximum winds. The global models indicate that this process will complete by 96 h. The new NHC intensity forecast is slightly higher than the previous forecast, but lies on the lower end of the intensity guidance for the first 72 h. It is near the consensus aids thereafter. FORECAST POSITIONS AND MAX WINDS INIT 11/2100Z 30.0N 36.1W 65 KT 75 MPH 12H 12/0600Z 30.3N 35.7W 70 KT 80 MPH 24H 12/1800Z 30.7N 35.2W 75 KT 85 MPH 36H 13/0600Z 31.4N 34.1W 75 KT 85 MPH 48H 13/1800Z 32.3N 31.9W 70 KT 80 MPH 72H 14/1800Z 35.5N 24.5W 70 KT 80 MPH 96H 15/1800Z 43.0N 16.0W 65 KT 75 MPH...POST-TROP/EXTRATROP 120H 16/1800Z 53.5N 10.5W 60 KT 70 MPH...POST-TROP/EXTRATROP $$ Forecaster Zelinsky

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Tropical Storm Ophelia Forecast Discussion Number 10

2017-10-11 16:40:05| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Wed Oct 11 2017 000 WTNT42 KNHC 111439 TCDAT2 Tropical Storm Ophelia Discussion Number 10 NWS National Hurricane Center Miami FL AL172017 1100 AM AST Wed Oct 11 2017 If I only had conventional satellite imagery, I would definitely estimate that Ophelia was a hurricane. The cyclone has a ragged eye surrounded by deep convection and cyclonically curved bands. Furthermore, Dvorak intensity estimates, both subjective and objective, from all agencies are T4.0 plus. However, several ASCAT passes during the past day or so indicate that the winds have been lower than the winds one could assign the cyclone by using Dvorak. Once again this morning, a pair of ASCAT passes showed winds of less than 45 kt, but I am assuming that the ASCAT can not resolve the sharp wind gradient typically associated with an eyewall, and earlier SSMIS data indicated that one is present. Since we do not have a hurricane hunter plane to give us exact measurements, we need to compromise between the very valuable satellite-based estimates, and the initial intensity is set at 60 kt in this advisory. Although the ocean is not too warm, the shear is low and the upper-troposphere is cool. These factors should provide some low-octane fuel favoring slight strengthening, and Ophelia is still expected to become a hurricane at any time within the next 12 hours. Extratropical transition is likely to start between day 3 and day 4, and Ophelia is anticipated to remain a strong cyclone over the northeastern Atlantic. Ophelia is moving slowly toward the east at 3 kt, embedded within light steering currents, and little motion is expected today. A mid-level trough is forecast to amplify west of Ophelia, and this pattern will provide a stronger southwesterly steering flow which eventually force the cyclone to move toward the northeast with increasing forward speed. Most of the track models agree with this solution increasing the confidence in the track forecast. The NHC forecast follows very closely the HFIP corrected consensus HCCA which has been very skillful this season. FORECAST POSITIONS AND MAX WINDS INIT 11/1500Z 30.0N 36.5W 60 KT 70 MPH 12H 12/0000Z 29.9N 36.0W 65 KT 75 MPH 24H 12/1200Z 30.1N 35.7W 70 KT 80 MPH 36H 13/0000Z 30.8N 34.7W 70 KT 80 MPH 48H 13/1200Z 31.5N 33.3W 70 KT 80 MPH 72H 14/1200Z 34.0N 26.8W 70 KT 80 MPH 96H 15/1200Z 40.0N 17.5W 70 KT 80 MPH...POST-TROP/EXTRATROP 120H 16/1200Z 51.5N 12.5W 60 KT 70 MPH...POST-TROP/EXTRATROP $$ Forecaster Avila

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