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Post-Tropical Cyclone ROSLYN Forecast Discussion Number 17
2016-09-29 16:54:11| National Hurricane Center (East Pacific)
Issued at 800 AM PDT THU SEP 29 2016 000 WTPZ43 KNHC 291453 TCDEP3 POST-TROPICAL CYCLONE ROSLYN DISCUSSION NUMBER 17 NWS NATIONAL HURRICANE CENTER MIAMI FL EP182016 800 AM PDT THU SEP 29 2016 Roslyn has been devoid of deep convection overnight, and the system consists of only a swirl of low clouds. Given the lack of convection, Roslyn has become a post-tropical remnant low. The initial intensity is kept at 25 kt based on continuity from earlier scatterometer data. The cyclone should spin down over cool waters and completely dissipate after 24 hours. The motion is north-northwestward or 345/6 kt. A weak low-level ridge to the north and northwest of the system should cause a turn toward the northwest and west-northwest until dissipation. This is the last advisory on Roslyn. For additional information on the remnant low please see High Seas Forecasts issued by the National Weather Service, under AWIPS header NFDHSFEPI, WMO header FZPN02 KWBC, and on the web at http://www.opc.ncep.noaa.gov/shtml/NFDHSFEPI.shtml. FORECAST POSITIONS AND MAX WINDS INIT 29/1500Z 23.5N 115.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 12H 30/0000Z 24.1N 116.2W 20 KT 25 MPH...POST-TROP/REMNT LOW 24H 30/1200Z 24.4N 117.4W 15 KT 15 MPH...POST-TROP/REMNT LOW 36H 01/0000Z...DISSIPATED $$ Forecaster Pasch
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Tropical Storm MATTHEW Forecast Discussion Number 4
2016-09-29 11:05:32| National Hurricane Center (Atlantic)
Issued at 500 AM AST THU SEP 29 2016 000 WTNT44 KNHC 290905 TCDAT4 TROPICAL STORM MATTHEW DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL AL142016 500 AM AST THU SEP 29 2016 Matthew is currently experiencing 15-20 kt of southwesterly vertical wind shear, with the low-level center located near the western edge of the main convective mass. An earlier Air Force Reserve Hurricane Hunter mission reported 850 mb flight-level winds of 65-70 kt and estimated surface winds of 50-55 kt from the SFMR instrument. Based on these data, the initial intensity remains 55 kt. The aircraft reported a central pressure of 1002 mb on its last pass through the center. The initial motion is 275/14. Matthew is currently on the south side of a low- to mid-level subtropical ridge. This feature should steer the storm westward or even south of west during the next 48 hours. After that time, Matthew is expected to approach the western end of the ridge as a mid- to upper-level trough develops over the Gulf of Mexico. While this combination is expected to cause the cyclone to turn generally northward, there is significant disagreement between the dynamical models on where the turn will occur and how fast Matthew will move northward. The forecast track is in best agreement with the GFS and GFS ensemble mean in bringing the center to eastern Cuba by 120 hours, although it is slower than those models. The Canadian model is a little west of the forecast track. The ECMWF and UKMET are to the east of the forecast track and much slower, bringing the center to the island of Hispaniola. Overall, the new forecast track is nudged a little south of the previous track for the first 72 hours, then is similar to the previous track. Users are reminded that the average NHC track errors at days 4 and 5 are on the order of 180 and 240 miles, respectively. The current shear is likely to gradually diminish during the next 72 hours, and this should allow continued gradual development. After that time, there is also disagreement in the models regarding the forecast shear, with the GFS showing a more favorable pattern than the ECMWF. If the GFS upper-level winds are correct, Matthew could strengthen more than currently forecast as show by the HWRF. However, given the uncertainty, the new intensity forecast is the same as the previous forecast and is in best agreement with the intensity consensus. FORECAST POSITIONS AND MAX WINDS INIT 29/0900Z 14.0N 64.7W 55 KT 65 MPH 12H 29/1800Z 14.1N 66.7W 60 KT 70 MPH 24H 30/0600Z 14.1N 69.2W 65 KT 75 MPH 36H 30/1800Z 13.9N 70.8W 70 KT 80 MPH 48H 01/0600Z 13.8N 72.2W 75 KT 85 MPH 72H 02/0600Z 14.5N 74.0W 75 KT 85 MPH 96H 03/0600Z 17.5N 75.0W 85 KT 100 MPH 120H 04/0600Z 20.5N 75.5W 80 KT 90 MPH...INLAND $$ Forecaster Beven
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Tropical Storm ULIKA Forecast Discussion Number 12
2016-09-29 10:51:36| National Hurricane Center (East Pacific)
Issued at 200 AM PDT THU SEP 29 2016 000 WTPZ44 KNHC 290851 TCDEP4 TROPICAL STORM ULIKA DISCUSSION NUMBER 12 NWS NATIONAL HURRICANE CENTER MIAMI FL EP192016 200 AM PDT THU SEP 29 2016 Despite about 25 kt of west-southwesterly shear, a burst of deep convection which developed around 0100 UTC has persisted, and Dvorak final-T numbers from TAFB and SAB increased to T3.5/55 kt and T2.0/30 kt, respectively. Based on these numbers, the initial intensity is held at 45 kt. Vertical shear is expected to turn westerly and increase to between 30 and 50 kt during the next couple of days. Given Ulika's small size, it will be no match for this type of shear and should therefore weaken very quickly. The NHC intensity forecast decays the system very similarly to what is shown by the LGEM model. Based on the latest global model fields, Ulika is likely to dissipate by day 3, if not sooner. Ulika has turned north-northwestward, or 340/5 kt, around the eastern side of a mid-level low located near 19N144W. The cyclone is expected to continue turning counterclockwise around this feature today and tonight, and it should then be moving westward by Friday when it is steered by lower-level trade wind flow. The updated NHC track forecast is a little west and south of the previous forecast, but that is primarily due to an adjustment of the initial position. FORECAST POSITIONS AND MAX WINDS INIT 29/0900Z 16.0N 139.1W 45 KT 50 MPH 12H 29/1800Z 16.7N 139.7W 35 KT 40 MPH 24H 30/0600Z 17.4N 140.7W 30 KT 35 MPH 36H 30/1800Z 17.6N 142.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 01/0600Z 17.5N 144.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 02/0600Z...DISSIPATED $$ Forecaster Berg
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Tropical Depression ROSLYN Forecast Discussion Number 15
2016-09-29 04:57:07| National Hurricane Center (East Pacific)
Issued at 800 PM PDT WED SEP 28 2016 000 WTPZ43 KNHC 290256 TCDEP3 TROPICAL DEPRESSION ROSLYN DISCUSSION NUMBER 15 NWS NATIONAL HURRICANE CENTER MIAMI FL EP182016 800 PM PDT WED SEP 28 2016 A small area of deep convection continues to fire to the north of the center of the cyclone, with little change in Roslyn during the past several hours. The initial wind speed is held at 30 kt in accordance with the past ASCAT data. The cyclone should move over progressively cooler water in a strongly sheared and dry environment. Thus, weakening should occur, and the new forecast is an update of the previous one, showing Roslyn decaying to a remnant low in 12 hours. The depression continues moving northward, now at 6 kt. Roslyn should turn northwestward and then westward before dissipation in about 2 days while the shallow cyclone becomes increasingly steered by a low-level ridge to the north. The new track forecast is a little slower than and south of the previous one since the latest guidance has trended in that direction. FORECAST POSITIONS AND MAX WINDS INIT 29/0300Z 22.1N 115.1W 30 KT 35 MPH 12H 29/1200Z 22.8N 115.4W 25 KT 30 MPH...POST-TROP/REMNT LOW 24H 30/0000Z 23.2N 116.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 36H 30/1200Z 23.2N 116.7W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 01/0000Z...DISSIPATED $$ Forecaster Blake
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Tropical Storm MATTHEW Forecast Discussion Number 3
2016-09-29 04:52:06| National Hurricane Center (Atlantic)
Issued at 1100 PM AST WED SEP 28 2016 000 WTNT44 KNHC 290251 TCDAT4 TROPICAL STORM MATTHEW DISCUSSION NUMBER 3 NWS NATIONAL HURRICANE CENTER MIAMI FL AL142016 1100 PM AST WED SEP 28 2016 Matthew crossed a portion of the Lesser Antilles today, and tropical-storm-force winds were experienced in various islands for several hours. The strongest winds appeared to have occurred in Martinique which was located in the northeastern quadrant of the storm. An Air Force plane currently investigating Matthew measured a peak wind at 850-mb of 73 kt, while the SFMR instrument measured 54 kt. The minimum central pressure was 1004 mb. There are no signs of an inner core yet, but the cloud pattern has increased in organization, and the initial intensity was adjusted upward to 55 kt. Matthew is forecast to move over warm waters and relatively low shear during the next few days, and these conditions should lead to gradual strengthening. There is a possibility, however, that Matthew encounters some westerly shear in the central Caribbean well south of Haiti in a day or two. This is an area climatologically unfavorable for storms to intensify, and Matthew could reduce its rate of strengthening there. After that, most of the models show a more conducive upper-level environment, and Matthew could intensify at a faster rate. The NHC forecast is not very different from its predecessor and follows closely the intensity consensus. Fixes from an Air Force plane indicate that Matthew is moving toward the west or 270 degrees at 13 kt. A strong subtropical ridge over the Atlantic is steering Matthew westward, and some models even move the cyclone south of due west. Most of the guidance is very consistent with this track during the next 48 hours. After that time, guidance becomes more divergent, but in general, all models turn the cyclone toward the northwest and north. Of the historically reliable models, the westernmost track is the ECMWF ensemble mean while the easternmost is the HWRF. The NHC track forecast is in the middle of the TVCX and TVCN multi-model consensus, and does not depart very much from the previous official forecast. There will be very interesting days ahead as Matthew moves toward the central and western Caribbean Sea, and users are reminded that the average NHC track errors at days 4 and 5 are on the order of 180 and 240 miles, respectively. FORECAST POSITIONS AND MAX WINDS INIT 29/0300Z 13.9N 63.1W 55 KT 65 MPH 12H 29/1200Z 14.3N 65.3W 60 KT 70 MPH 24H 30/0000Z 14.4N 67.9W 65 KT 75 MPH 36H 30/1200Z 14.3N 70.0W 70 KT 80 MPH 48H 01/0000Z 14.1N 71.5W 75 KT 85 MPH 72H 02/0000Z 14.5N 73.5W 75 KT 85 MPH 96H 03/0000Z 16.8N 75.0W 90 KT 105 MPH 120H 04/0000Z 20.0N 75.5W 90 KT 105 MPH $$ Forecaster Avila
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