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Tropical Storm Kirk Forecast Discussion Number 12

2018-09-26 22:32:29| National Hurricane Center (Atlantic)

Issued at 500 PM AST Wed Sep 26 2018 180 WTNT42 KNHC 262032 TCDAT2 Tropical Storm Kirk Discussion Number 12 NWS National Hurricane Center Miami FL AL122018 500 PM AST Wed Sep 26 2018 The storm's cloud pattern now has a more comma-shaped appearance, with the estimated center near the western edge of the comma head. Some low-cloud lines are becoming exposed over the western portion of the circulation, which is suggestive of some increase in vertical shear. Based on flight-level and uncontaminated SFMR winds from the Air Force Hurricane Hunter mission a few hours ago, the intensity is kept at 50 kt for this advisory. The dynamical guidance is in good agreement that the shear will increase significantly in 18 to 24 hours, and a weakening trend is likely to commence around that time. The system is predicted to dissipate due to the strong shear over the Caribbean Sea in about 5 days, and several of the reliable global models show this occurring even sooner. The official intensity forecast is similar to the latest multi-model consensus, IVCN, which has been a good performer in the Atlantic basin so far this year. Kirk is moving west-northwestward, or 285/16 kt. A pronounced mid-level ridge over the southwestern North Atlantic and Florida should continue to steer Kirk on a west-northwestward to westward heading through the forecast period. Based on the latest track model guidance, the official forecast is somewhat faster than the previous one and now takes Kirk over the Lesser Antilles in about 24 hours. On this basis, the arrival of tropical-storm-force winds in the warning area is a few hours earlier than implied by the previous advisory. For specific timing information, please consult the latest arrival time of tropical-storm-force winds graphic on the National Hurricane Center website. FORECAST POSITIONS AND MAX WINDS INIT 26/2100Z 12.7N 55.7W 50 KT 60 MPH 12H 27/0600Z 13.5N 57.9W 50 KT 60 MPH 24H 27/1800Z 14.4N 60.2W 45 KT 50 MPH 36H 28/0600Z 15.1N 62.5W 40 KT 45 MPH 48H 28/1800Z 15.7N 65.0W 35 KT 40 MPH 72H 29/1800Z 16.3N 70.0W 25 KT 30 MPH 96H 30/1800Z 15.7N 74.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 01/1800Z...DISSIPATED $$ Forecaster Pasch

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Hurricane Rosa Forecast Discussion Number 7

2018-09-26 22:32:29| National Hurricane Center (East Pacific)

Issued at 300 PM MDT Wed Sep 26 2018 178 WTPZ45 KNHC 262032 TCDEP5 Hurricane Rosa Discussion Number 7 NWS National Hurricane Center Miami FL EP202018 300 PM MDT Wed Sep 26 2018 Rosa continues to strengthen this afternoon. Improved deep convective banding features with -83C cloud tops are evident in both visible and microwave images, particularly in the east semicircle. The initial intensity is bumped up to 70 kt and is a compromise of the subjective and objective satellite intensity estimates. It still appears likely that Rosa will continue to quickly strengthen through this evening while it moves over warm oceanic temperatures and in a high moisture and low shear atmospheric environment. The official forecast is based on a blend of the IVCN and NOAA-HCCA intensity consensus models, and shows strengthening, at a slower pace, after the RI period. Beyond 48 hours, steady weakening is forecast due to decreasing sea surface temperatures, increasing southwesterly shear, and a high statically stable surrounding environment. Rosa is currently moving west-northwestward, or 285/9 kt, within the mid-level easterly steering flow produced by a mid-level ridge extending from northern Mexico westward over the eastern Pacific. At around day 3, Rosa is expect to move northwestward and then northward day 4 in response to a mid-latitude trough approaching from the northwest. The along track spread beyond day 3 continues to be an issue with the GFS global and HWRF hurricane model indicating a much more faster north to north-northeast motion than the slower European model cluster. In this scenario, the NHC forecast will remain near the better performing various multi-model consensus models. FORECAST POSITIONS AND MAX WINDS INIT 26/2100Z 16.5N 112.2W 70 KT 80 MPH 12H 27/0600Z 16.7N 113.6W 90 KT 105 MPH 24H 27/1800Z 16.9N 115.3W 100 KT 115 MPH 36H 28/0600Z 17.2N 116.7W 105 KT 120 MPH 48H 28/1800Z 17.8N 117.7W 110 KT 125 MPH 72H 29/1800Z 20.1N 119.4W 95 KT 110 MPH 96H 30/1800Z 23.3N 119.2W 80 KT 90 MPH 120H 01/1800Z 26.6N 117.5W 60 KT 70 MPH $$ Forecaster Roberts

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Tropical Storm Kirk Forecast Discussion Number 11

2018-09-26 16:58:27| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Wed Sep 26 2018 196 WTNT42 KNHC 261458 TCDAT2 Tropical Storm Kirk Discussion Number 11 NWS National Hurricane Center Miami FL AL122018 1100 AM AST Wed Sep 26 2018 Kirk is maintaining a CDO of strong convection over its center, but banding features are limited. Observations from an Air Force Reserve Unit Hurricane Hunter aircraft along with scatterometer data indicate that the storm has strengthened a little and the maximum winds are now near 45 kt. The SHIPS model output shows a large increase in westerly shear over Kirk within 18-24 hours. Therefore not much additional strengthening is likely, and a weakening trend should commence in a day or so. The official intensity forecast is similar to the latest model consensus. Strong westerly shear is likely to continue to adversely affect Kirk while it moves over the Caribbean, and the system should weaken into a depression within 72 hours or sooner, and become a remnant low later in the forecast period. The motion is a little north of due west, or 280/16 kt. The steering pattern for Kirk is rather straightforward. A subtropical high pressure area over the southwestern North Atlantic is expected to persist and retrograde slightly westward over the forecast period. The flow on the southern side of the high should steer Kirk on a westward to west-northwestward track for the next several days. The official track forecast is close to the corrected dynamical model consensus, HCCA, and is very similar to the previous NHC track. FORECAST POSITIONS AND MAX WINDS INIT 26/1500Z 12.1N 54.3W 45 KT 50 MPH 12H 27/0000Z 12.7N 56.1W 45 KT 50 MPH 24H 27/1200Z 13.7N 58.7W 45 KT 50 MPH 36H 28/0000Z 14.5N 61.0W 40 KT 45 MPH 48H 28/1200Z 15.2N 63.2W 35 KT 40 MPH 72H 29/1200Z 16.0N 68.0W 30 KT 35 MPH 96H 30/1200Z 16.0N 72.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 01/1200Z 16.0N 76.0W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Pasch

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Tropical Storm Rosa Forecast Discussion Number 5

2018-09-26 10:45:25| National Hurricane Center (East Pacific)

Issued at 300 AM MDT Wed Sep 26 2018 934 WTPZ45 KNHC 260845 TCDEP5 Tropical Storm Rosa Discussion Number 5 NWS National Hurricane Center Miami FL EP202018 300 AM MDT Wed Sep 26 2018 After steadily intensifying yesterday, Rosa's strengthening trend has temporarily paused. The tropical storm has a well-defined curved band that wraps about three-quarters of the way around the center. However, some dry air appears to be intruding into the core from the northeastern quadrant, which could be the reason why Rosa has stopped strengthening for now. The Dvorak classifications from TAFB and SAB remain 3.5/55 kt, so the initial intensity is held at that value. This wind speed is also close to the latest SATCON estimate from CIMSS at the University of Wisconsin. A strengthening trend is expected to resume soon, and it seems likely that Rosa will rapidly intensify during the next couple of days while it remains over warm SSTs and in an environment of low wind shear of 10 kt or less. The NHC intensity forecast closely follows the HCCA model, and brings Rosa to hurricane strength later today and major hurricane strength on Thursday. Beyond a few days, steady weakening is forecast due to cooler SSTs, dry and stable air, and an increase in southwesterly wind shear. The tropical storm is moving west-northwestward at 7 kt, steered by a mid-level ridge to its north. A west to west-northwest motion at about the same forward speed is expected for the next couple of days as the pattern holds. After that time, the ridge is expected to break down as a large, deep-layer low moves toward the U.S. west coast. This change in the steering flow should cause Rosa to move northwestward late Friday and Saturday and then northward late in the weekend. The models have come into a little better agreement this cycle, and a slight eastward shift has been made at 96- and 120-hours based on this guidance. This forecast lies fairly close to the various consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 26/0900Z 15.5N 110.4W 55 KT 65 MPH 12H 26/1800Z 15.9N 111.5W 70 KT 80 MPH 24H 27/0600Z 16.2N 113.2W 85 KT 100 MPH 36H 27/1800Z 16.5N 115.0W 100 KT 115 MPH 48H 28/0600Z 16.8N 116.7W 105 KT 120 MPH 72H 29/0600Z 18.3N 119.0W 105 KT 120 MPH 96H 30/0600Z 20.7N 120.3W 85 KT 100 MPH 120H 01/0600Z 23.0N 120.0W 65 KT 75 MPH $$ Forecaster Cangialosi

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Tropical Storm Kirk Forecast Discussion Number 10

2018-09-26 10:44:52| National Hurricane Center (Atlantic)

Issued at 500 AM AST Wed Sep 26 2018 961 WTNT42 KNHC 260844 TCDAT2 Tropical Storm Kirk Discussion Number 10 NWS National Hurricane Center Miami FL AL122018 500 AM AST Wed Sep 26 2018 Infrared satellite imagery during the past several hours indicates that deep convection has increased and become better organized near the center of the remnants of Kirk. In addition, two earlier ASCAT scatterometer passes between 0000-0100Z indicated that the low-level center had become a little better defined, and that the inner-core wind field had contracted, now with a radius of maximum winds (RMW) of about 40 nmi. Given the continued increase in the amount and organization of the deep convection, advisories have be re-initiated on Tropical Storm Kirk. The two ASCAT passes showed peak winds of 38 and 44 kt, so the initial intensity will be a blend of these two values or 40 kt. An Air Force Reserve reconnaissance aircraft will be investigating Kirk later this morning to provide more detailed information on the location and intensity of the tropical storm. The initial motion estimates is an uncertain 280/16 kt, due to the lack of a well-defined center to track for the past two days. The global and regional models, excluding the HWRF model, are in very good agreement on Kirk moving between west and west-northwest for the next 72 hours along the south side of a strong Bermuda-Azores high pressure system anchored across most of the subtropical Atlantic. After that time, strong shear is forecast to weaken Kirk into a remnant low, resulting in a more westward motion as the shallow cyclone will be steered by the low-level easterly trade wind flow. The official forecast track closely follows the HCCA corrected-consensus model, and is a little south of the simple consensus model TVCA due to an apparent northward bias in the HWRF member. The current modest west to southwesterly vertical wind shear is forecast to decrease to less than 10 kt during the next 24 hours, which should allow for some slight strengthening to occur. After 48 hours when Kirk is forecast to emerge over the eastern Caribbean Sea, the shear is expected to increase to more then 30 kt, which should act to displace the deep convection to the east of the low-level center, resulting in rapid weakening. Kirk is forecast to degenerate into a remnant low pressure system after 72 hours, but this could occur a little sooner than indicated in the official forecast if Kirk moves farther north and into even stronger shear conditions. The NHC intensity forecast closely follows a blend of the HCCA, FSSE, and IVCN consensus models. FORECAST POSITIONS AND MAX WINDS INIT 26/0900Z 11.8N 52.7W 40 KT 45 MPH 12H 26/1800Z 12.4N 55.0W 45 KT 50 MPH 24H 27/0600Z 13.2N 57.6W 45 KT 50 MPH 36H 27/1800Z 14.1N 60.0W 45 KT 50 MPH 48H 28/0600Z 14.8N 62.3W 40 KT 45 MPH 72H 29/0600Z 15.7N 67.0W 30 KT 35 MPH 96H 30/0600Z 15.9N 71.6W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 01/0600Z 16.0N 76.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Stewart

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