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Tropical Storm Ophelia Forecast Discussion Number 9

2017-10-11 10:36:31| National Hurricane Center (Atlantic)

Issued at 500 AM AST Wed Oct 11 2017 000 WTNT42 KNHC 110836 TCDAT2 Tropical Storm Ophelia Discussion Number 9 NWS National Hurricane Center Miami FL AL172017 500 AM AST Wed Oct 11 2017 Ophelia has become better organized during the past several hours, with convective banding now wrapping almost all of the way around the center. Satellite intensity estimates from TAFB and SAB have increased to 55 kt and 65 kt, respectively, and several recent microwave-based intensity estimates are in the 55-65 kt range. Based on this, the initial intensity is increased to a possibly conservative 55 kt. The initial motion is now 125/5. Ophelia should continue to move southeastward or east-southeastward during the next 12-24 hours with a decrease in forward speed while it remains embedded within a mid- to upper-level trough to the south of the mid-latitude westerlies. After that, the cyclone is forecast to turn northeastward and accelerate by day 3 ahead of a deepening mid-latitude trough over the north-central Atlantic. The latest track guidance is in good agreement with this scenario. However, there has been a significant northward shift in the 120 h forecasts since the last advisory. The new official forecast track is similar to the previous track through 72 h, and then is adjusted northward at the 96 and 120 h points. It should be noted, though, that the 120 h point is to the south of the consensus and large-scale models, and additional northward adjustments may be required later. The cyclone is expected to be within a low shear environment and over marginally warm sea surface temperatures during the next 2 to 3 days. These conditions favor strengthening and the NHC forecast now calls for Ophelia to become a hurricane in about 24 hours. Extratropical transition is likely to start around day 4 and be complete by day 5, with the associated baroclinic dynamics expected to keep Ophelia a strong cyclone over the northeastern Atlantic. FORECAST POSITIONS AND MAX WINDS INIT 11/0900Z 30.2N 37.0W 55 KT 65 MPH 12H 11/1800Z 29.9N 36.4W 60 KT 70 MPH 24H 12/0600Z 30.1N 35.9W 65 KT 75 MPH 36H 12/1800Z 30.5N 35.3W 75 KT 85 MPH 48H 13/0600Z 31.2N 34.0W 75 KT 85 MPH 72H 14/0600Z 33.5N 28.5W 70 KT 80 MPH 96H 15/0600Z 37.5N 20.5W 70 KT 80 MPH 120H 16/0600Z 43.0N 13.0W 65 KT 75 MPH...POST-TROP/EXTRATROP $$ Forecaster Beven

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Tropical Storm Ophelia Forecast Discussion Number 8

2017-10-11 04:36:30| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Tue Oct 10 2017 000 WTNT42 KNHC 110236 TCDAT2 Tropical Storm Ophelia Discussion Number 8 NWS National Hurricane Center Miami FL AL172017 1100 PM AST Tue Oct 10 2017 Ophelia has lost some of its outer banding this evening, but a well-defined band of convection remains over the southeastern and southern portion of the circulation. A 2322 UTC ASCAT overpass again suggests that the winds are not as strong what is indicated by the Dvorak satellite estimates. The highest winds in the ASCAT pass were 35 kt, but with some undersampling consideration the initial intensity is set to 45 kt. Ophelia is moving southeastward or 140/5 kt. The cyclone should continue to move southeastward or east-southeastward during the next 24 hours while it remains embedded within a mid- to upper-level trough. After that time, Ophelia is forecast to turn eastward, then northeastward and begin to accelerate by day 3 ahead of a deepening mid-latitude trough over the north-central Atlantic. The latest run of the GFS shifted eastward and is very similar to the 12Z ECMWF, and the previous NHC track forecast. These typically reliable models are along the southern edge of the track envelope, and the NHC forecast remains there as well. The cyclone is expected to be within a low shear environment and over marginally warm sea surface temperatures during the next 2 to 3 days. These conditions favor strengthening and the NHC forecast again calls for Ophelia to become a hurricane in about 36 hours, although the forecast wind speed through 24 hours is slightly less than the previous advisory due to the lower initial intensity. Later in the period, baroclinic dynamics are expected to keep Ophelia a strong cyclone over the northeastern Atlantic through day 5 when the system is forecast to become fully extratropical. FORECAST POSITIONS AND MAX WINDS INIT 11/0300Z 30.7N 37.6W 45 KT 50 MPH 12H 11/1200Z 30.3N 37.0W 50 KT 60 MPH 24H 12/0000Z 30.1N 36.5W 55 KT 65 MPH 36H 12/1200Z 30.2N 36.0W 65 KT 75 MPH 48H 13/0000Z 30.7N 35.0W 70 KT 80 MPH 72H 14/0000Z 32.5N 30.8W 70 KT 80 MPH 96H 15/0000Z 35.7N 23.2W 70 KT 80 MPH 120H 16/0000Z 41.0N 14.0W 65 KT 75 MPH...POST-TROP/EXTRATROP $$ Forecaster Brown

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Tropical Storm Ophelia Forecast Discussion Number 7

2017-10-10 22:39:26| National Hurricane Center (Atlantic)

Issued at 500 PM AST Tue Oct 10 2017 000 WTNT42 KNHC 102039 TCDAT2 Tropical Storm Ophelia Discussion Number 7 NWS National Hurricane Center Miami FL AL172017 500 PM AST Tue Oct 10 2017 The overall convective structure of Ophelia has improved markedly over the past several, including the development of numerous, tightly curved bands and a burst of deep convection near the center. Upper-level anticyclonic outflow has also increased and expanded in all quadrants. Dvorak satellite current intensity estimates are T3.5/55 kt from TAFB and T4.0/65 kt from SAB, so the initial intensity has been conservatively increased to 50 kt. A 28-30 kt wind report from ship PBQL, located more 200 nmi northwest of the center, indicates that the outer circulation is also strengthening. The initial motion estimate is 135/04 kt. Ophelia is forecast to continue moving southeastward at a slow but steady pace for the next 48 hours or so while the cyclone remains embedded within a broad mid-/upper-level trough. The NHC model guidance remains in good agreement on the Ophelia beginning to lift out to the northeast by 72 h, and then gradually accelerate into the mid-latitude westerlies ahead of an eastward-moving mid-tropospheric trough. The latest model guidance remains tightly packed, but it has also shifted northward, which brings Ophelia closer to the Azores in the 96-120 hour period. However, the new forecast track was not shifted northward and remains along the southern edge of the guidance envelope between the NOAA HCCA consensus model and the more southerly ECMWF model. The GFS and ECMWF models continue to forecast only modest intensification for the next 48-72 hours, despite the vertical wind shear being fairly low at less than 10 kt. However, those models are forecasting more vigorous strengthening after 96 h as Ophelia experiences some baroclinic interaction, especially by 120 hours. The strong baroclinic deepening on day 5 could be overdone somewhat given that the best jetstream dynamics are forecast to be about 300 nmi northwest of the surface low and frontal zone. For now, the official intensity forecast remains similar to the previous advisory, and is little lower than the intensity consensus models HCCA and IVCN and the GFS and ECMWF solutions on days 4 and 5. FORECAST POSITIONS AND MAX WINDS INIT 10/2100Z 31.1N 38.0W 50 KT 60 MPH 12H 11/0600Z 30.6N 37.5W 55 KT 65 MPH 24H 11/1800Z 30.2N 36.8W 60 KT 70 MPH 36H 12/0600Z 30.2N 36.4W 65 KT 75 MPH 48H 12/1800Z 30.5N 35.6W 70 KT 80 MPH 72H 13/1800Z 32.0N 32.2W 70 KT 80 MPH 96H 14/1800Z 34.7N 25.8W 70 KT 80 MPH 120H 15/1800Z 39.0N 17.0W 70 KT 80 MPH...POST-TROP/EXTRATROP $$ Forecaster Stewart

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Tropical Storm Ophelia Forecast Discussion Number 6

2017-10-10 16:59:28| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Tue Oct 10 2017 000 WTNT42 KNHC 101459 TCDAT2 Tropical Storm Ophelia Discussion Number 6 NWS National Hurricane Center Miami FL AL172017 1100 AM AST Tue Oct 10 2017 Convective banding has continued to become better defined since the previous advisory, and an eye-like feature has developed in the center of the convection. However, despite the much improved satellite appearance, it appears that the increased convective organization has not yet translated into an increase in the surface winds based on a 1204Z ASCAT-B overpass, which only showed winds of 30-31 kt in the southern quadrant. Some undersampling is likely due to the small 25-nmi radius of maximum winds, and two nearby ships were under-sampled by at least 5 kt. Dvorak intensity estimates range from T2.3/33 kt from UW-CIMSS to T3.0/45 kt from TAFB to T4.0/65 kt from SAB. For now, the initial intensity will remain at 45 kt, which is an average of the scatterometer winds and all of the other available intensity estimates. Ophelia has been lumbering along slowly toward the southeast during the past 6 hours, and the initial motion estimate is now 130/04 kt. The latest model guidance remains in excellent agreement on the cyclone moving slowly toward the southeast for next 48 hours or so. By 72 hours, Ophelia is expected to turn northeastward and gradually accelerate into the westerlies ahead of a deep-layer trough. Since the NHC model guidance is tightly packed about the previous advisory track, only minor adjustments were made for this advisory. The intensity forecast isn't as straightforward as the track forecast due to the aforementioned differences in the intensity estimates. However, given that both the GFS and ECMWF models accurately predicted much lower intensity values of 35-40 kt for the 1200Z initial time period, a blend of those models were used to construct the intensity forecast for this advisory package. In addition to the slightly lower intensity forecast, the wind radii were also decreased both at the initial time and throughout the forecast period. FORECAST POSITIONS AND MAX WINDS INIT 10/1500Z 31.5N 38.3W 45 KT 50 MPH 12H 11/0000Z 30.9N 37.9W 50 KT 60 MPH 24H 11/1200Z 30.2N 37.4W 55 KT 65 MPH 36H 12/0000Z 29.8N 36.9W 60 KT 70 MPH 48H 12/1200Z 30.0N 36.2W 65 KT 75 MPH 72H 13/1200Z 31.2N 33.8W 70 KT 80 MPH 96H 14/1200Z 33.4N 28.5W 70 KT 80 MPH 120H 15/1200Z 36.0N 21.5W 70 KT 80 MPH...POST-TROP/EXTRATROP $$ Forecaster Stewart

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Tropical Storm Ophelia Forecast Discussion Number 5

2017-10-10 10:31:55| National Hurricane Center (Atlantic)

Issued at 500 AM AST Tue Oct 10 2017 000 WTNT42 KNHC 100831 TCDAT2 Tropical Storm Ophelia Discussion Number 5 NWS National Hurricane Center Miami FL AL172017 500 AM AST Tue Oct 10 2017 Although the intensity of Ophelia's deep convection has decreased during the past several hours, the cloud pattern has improved and become more symmetric with banding features now better established around the center. The initial intensity is held at 45 kt, in agreement with a Dvorak classification from SAB and the latest satellite consensus estimate from CIMSS at the University of Wisconsin. The recent decrease in convection could be associated with some dry air that has wrapped into the circulation, as seen in total precipitable water imagery. The other environmental conditions appear generally conducive for strengthening with wind shear values expected to decrease to near 10 kt during the next couple of days with SSTs remaining marginally warm around 26.5 to 27 deg C. These conditions combined with an unstable atmosphere should allow Ophelia to strengthen, and the NHC forecast follows the IVCN and HCCA consensus models and brings the cyclone to hurricane strength in 24 to 36 hours. Although the official forecast shows slight weakening by the end of the period due to an increase in shear and cooler waters, the latest guidance suggests that the weakening could be less than currently forecast. Satellite fixes indicate that Ophelia has made a turn to the southeast, as expected. A continued slow southeast motion is forecast during the next 36 to 48 hours as mid-level ridging builds to the north and west of the storm. After that time, a turn to the northeast or east-northeast at a progressively faster pace is expected as a mid- to upper-level trough approaches Ophelia. The models are in fairly good agreement, and only minor changes were made to the previous NHC track forecast. This prediction lies near the middle of the guidance envelope. FORECAST POSITIONS AND MAX WINDS INIT 10/0900Z 31.9N 38.8W 45 KT 50 MPH 12H 10/1800Z 31.7N 38.4W 55 KT 65 MPH 24H 11/0600Z 30.8N 37.9W 60 KT 70 MPH 36H 11/1800Z 30.2N 37.4W 70 KT 80 MPH 48H 12/0600Z 30.0N 36.8W 75 KT 85 MPH 72H 13/0600Z 31.0N 35.0W 75 KT 85 MPH 96H 14/0600Z 33.0N 30.5W 75 KT 85 MPH 120H 15/0600Z 35.5N 23.5W 65 KT 75 MPH $$ Forecaster Cangialosi

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