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Tropical Depression Eleven Forecast Discussion Number 6
2020-08-13 04:36:40| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Wed Aug 12 2020 000 WTNT41 KNHC 130236 TCDAT1 Tropical Depression Eleven Discussion Number 6 NWS National Hurricane Center Miami FL AL112020 1100 PM AST Wed Aug 12 2020 Conventional satellite imagery and a fortuitous ASCAT-B scatterometer overpass indicate that the center of circulation is a little farther south than previously estimated and remains well to the southeast of the deep convective canopy. The latest UW-CIMSS shear analysis confirms modest east-southeasterly shear impinging on the cloud pattern. A compromise of the satellite intensity estimates from TAFB and SAB, and the aforementioned scatterometer pass retains the initial intensity at 30 kt. Large-scale models and the statistical-dynamical intensity guidance still show the shear abating soon which should result in gradual strengthening with a peak intensity of 50 kt in 2 days. After that time, the cyclone is forecast to encounter moderate to strong southwesterly shear associated with a deep-layer trough stretching over the southwestern Atlantic. This change in the upper wind pattern should induce steady weakening. A number of the global models indicate that the cyclone will become a remnant low by day 4 and open up into a trough by day 5 which is certainly possible. The NHC forecast is similar to the previous advisory but indicates a more expeditious weakening trend beyond the 48 hour period in deference to the global model solution. The initial motion is estimated to be westward, or 275/13 kt, within the low to mid-tropospheric easterly flow produced by a subtropical ridge anchored to the north of the depression. The song remains the same...there is virtually no change to the forecast philosophy and only a slight shift to the left of the previous track forecast was made in response to the southward initial position adjustment. FORECAST POSITIONS AND MAX WINDS INIT 13/0300Z 12.5N 47.1W 30 KT 35 MPH 12H 13/1200Z 13.0N 48.4W 35 KT 40 MPH 24H 14/0000Z 14.2N 51.0W 40 KT 45 MPH 36H 14/1200Z 15.7N 53.7W 45 KT 50 MPH 48H 15/0000Z 17.0N 56.4W 50 KT 60 MPH 60H 15/1200Z 18.3N 58.9W 45 KT 50 MPH 72H 16/0000Z 19.7N 61.4W 40 KT 45 MPH 96H 17/0000Z 22.5N 65.6W 35 KT 40 MPH 120H 18/0000Z 25.6N 67.5W 30 KT 35 MPH $$ Forecaster Roberts
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Post-Tropical Cyclone Elida Forecast Discussion Number 17
2020-08-13 04:36:06| National Hurricane Center (East Pacific)
Issued at 800 PM PDT Wed Aug 12 2020 000 WTPZ44 KNHC 130235 TCDEP4 Post-Tropical Cyclone Elida Discussion Number 17 NWS National Hurricane Center Miami FL EP092020 800 PM PDT Wed Aug 12 2020 Elida has been devoid of deep convection for more than 12 hours, and since it is over SSTs of 22-23 degrees Celsius, it is unlikely that organized deep convection will return. As a result, the system has become a post-tropical cyclone, and this will be the last NHC advisory on Elida. The initial intensity has been set at 35 kt, which is a blend of the latest Dvorak T- and CI-numbers from TAFB and SAB. The cyclone is heading toward even cooler waters and a more stable environment. Continued weakening is therefore expected, and the remnant low is forecast to dissipate by Friday morning. The initial motion estimate is 315/8 kt. A low- to mid-level trough located to the northwest of the cyclone has caused a break in the subtropical ridge. This has allowed the system to turn northwestward, and a northwestward to north-northwestward motion is expected to continue until dissipation occurs on Friday. The global model guidance continues to suggest that the low-level center will decelerate as the mid-level circulation is pulled northward ahead of the aforementioned trough. The new NHC track foreast is similar to the previous advisory and again shows a slower forward motion than the global model trackers. This is the last NHC advisory on Elida. For additional information on this system please see High Seas Forecasts issued by the National Weather Service, under AWIPS header NFDHSFEPI, WMO header FZPN02 KWBC, and on the web at ocean.weather.gov/shtml/NFDHSFEPI.php FORECAST POSITIONS AND MAX WINDS INIT 13/0300Z 24.4N 120.2W 35 KT 40 MPH...POST-TROPICAL 12H 13/1200Z 25.3N 121.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 24H 14/0000Z 26.6N 121.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 36H 14/1200Z...DISSIPATED $$ Forecaster Brown
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Tropical Storm Elida Forecast Discussion Number 16
2020-08-12 22:37:04| National Hurricane Center (East Pacific)
Issued at 200 PM PDT Wed Aug 12 2020 000 WTPZ44 KNHC 122036 TCDEP4 Tropical Storm Elida Discussion Number 16 NWS National Hurricane Center Miami FL EP092020 200 PM PDT Wed Aug 12 2020 Elida's last remaining deep convection dissipated just after the issuance of the previous advisory, brought on by cold ocean water of only 22-23 degrees Celsius. Of the two ASCAT passes near the cyclone today, neither caught the likely area of strongest winds. Therefore, the maximum winds are lowered to 45 kt based on a blend of subjective estimates between 45-55 kt and objective numbers between 30-40 kt. Cold water and increasing shear should continue Elida's quick weakening trend, and the cyclone is expected to degenerate into a remnant low by tonight, barring the unlikely chance that deep convection redevelops. The remnant low is then forecast to dissipate in 48 hours in accordance with global model guidance. The initial motion is still west-northwestward, or 295/10 kt. A low- to mid-level trough extending southwest of California, which has caused a break in the subtropical ridge, is expected to allow Elida to turn northwestward and then north-northwestward soon. This forecast reasoning has not changed, however one change to the new NHC track forecast is that it is not as fast as is being shown by the model trackers. Global model fields suggest that Elida's low- to mid-level circulation will get pulled northward by increasing shear (which is reflected by the model trackers), leaving the surface circulation to the south. Given this discrepancy, the NHC forecast is to the south of most of the guidance to account for the actual location of the surface center. FORECAST POSITIONS AND MAX WINDS INIT 12/2100Z 23.7N 119.6W 45 KT 50 MPH 12H 13/0600Z 24.5N 120.6W 30 KT 35 MPH...POST-TROP/REMNT LOW 24H 13/1800Z 25.8N 121.4W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 14/0600Z 27.2N 121.9W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 14/1800Z...DISSIPATED $$ Forecaster Berg
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Tropical Depression Eleven Forecast Discussion Number 4
2020-08-12 16:43:00| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Wed Aug 12 2020 000 WTNT41 KNHC 121442 TCDAT1 Tropical Depression Eleven Discussion Number 4 NWS National Hurricane Center Miami FL AL112020 1100 AM AST Wed Aug 12 2020 Satellite imagery indicates that the depression is a little better organized than 24 h ago, with a ragged central convective feature and a curved convective band in the northwestern semicircle. However, recent scatterometer data show this has not yet resulted in strengthening, with 25-30 kt winds occuring to the north of the center. Based on the scatterometer, the initial intensity remains 30 kt. The initial motion remains a little north of due west, or 280/13 kt. There is little change to the forecast philosophy or the forecast track since the last advisory. A westward motion is expected to continue through tonight due to easterly flow on the south side of a strong subtropical ridge situated to the north of the cyclone. After that, the global models forecast a slight weakness to develop within the ridge, allowing the cyclone to turn west-northwestward, with that motion continuing through the end of the forecast period. The new NHC forecast is just to the left of the various consensus models. The southeasterly shear that has so far prevented intensification should diminish in the next 12 h or so, which should allow the cyclone to become a tropical storm. The system should then remain in light to moderate shear through about 48 h, and the intensity forecast calls for a peak intensity of 50 kt during that time. Later in the forecast period, moderate to strong southwesterly shear should develop over the cyclone due to an upper-level trough over the southwestern Atlantic. This shear should cause the system to weaken, and several of the global models forecast it to degenerate to a tropical wave before 120 h. The new intensity forecast will not call for that quick of a demise, but will show weakening due to the shear after 72 h. The new forecast, which has only minor changes from the previous forecast, is near the upper edge of the intensity guidance. FORECAST POSITIONS AND MAX WINDS INIT 12/1500Z 12.4N 44.2W 30 KT 35 MPH 12H 13/0000Z 12.8N 46.1W 35 KT 40 MPH 24H 13/1200Z 13.5N 48.4W 40 KT 45 MPH 36H 14/0000Z 14.5N 50.8W 45 KT 50 MPH 48H 14/1200Z 15.7N 53.3W 50 KT 60 MPH 60H 15/0000Z 17.0N 55.7W 50 KT 60 MPH 72H 15/1200Z 18.2N 58.1W 50 KT 60 MPH 96H 16/1200Z 20.5N 63.0W 40 KT 45 MPH 120H 17/1200Z 23.5N 66.5W 35 KT 40 MPH $$ Forecaster Beven
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Tropical Depression Eleven Forecast Discussion Number 3
2020-08-12 11:00:28| National Hurricane Center (Atlantic)
Issued at 500 AM AST Wed Aug 12 2020 000 WTNT41 KNHC 120900 TCDAT1 Tropical Depression Eleven Discussion Number 3 NWS National Hurricane Center Miami FL AL112020 500 AM AST Wed Aug 12 2020 After an earlier burst of deep convection near the center and in the western semicircle of the circulation, overall thunderstorm activity has decreased somewhat. This is likely due to the entrainment of mid-/upper-level dry air as noted in GOES-16 high-resolution mid- and upper-level water vapor imagery, in conjunction with some modest southeasterly vertical wind shear. The latest subjective and objective Dvorak satellite classifications from TAFB/SAB and UW-CIMSS ADT of 30 kt and 33 kt, respectively, support maintaining an initial intensity of 30 kt. The depression continues moving a little north of due west, or 280/13 kt. This general motion is expected to continue through tonight due to easterly flow on the south side of a strong subtropical ridge situated to the north of the cyclone. By 24 h, all of the global models are in decent agreement that a slight weakness will develop within the ridge, allowing the cyclone to turn more toward the west-northwest and then continue that motion through the end of the forecast period. The latest NHC model guidance is tightly packed about the previous forecast track, so no significant track changes were made. The aforementioned unfavorable conditions of dry air entrainment and southeasterly shear are expected to give way to more conducive environmental conditions by 24 h when the cyclone will begin to move underneath the center of a synoptic-scale upper-level anticyclone. This will result in the shear decreasing to near zero, along with a pronounced improvement in the upper-level outflow pattern. The much lower shear conditions should also reduce the amount of dry air entrainment, while allowing for some moistening of the surrounding environment to occur. These more favorable conditions are expected to persist through at least the 60-h period, and thus slow but steady strengthening is forecast during that time. By 72 h and beyond, the global models and regional models show the system moving out from underneath the positive influence of the upper-level anticyclone, encountering moderate southerly to southwesterly vertical wind shear, which is expected to induce gradual weakening. It should be noted that during the 48-60 h period when the shear will be the lowest and sea-surface temperatures will be near 28.5C, there is a narrow window of opportunity where the intensity could peak higher than what is currently indicated. The new NHC intensity forecast is very similar to the previous advisory, and is slightly higher than the consensus intensity consensus models IVCN and HCCA due to anticipation of the very favorable low-shear conditions. FORECAST POSITIONS AND MAX WINDS INIT 12/0900Z 12.2N 42.9W 30 KT 35 MPH 12H 12/1800Z 12.6N 44.8W 35 KT 40 MPH 24H 13/0600Z 13.2N 47.3W 40 KT 45 MPH 36H 13/1800Z 14.0N 49.6W 45 KT 50 MPH 48H 14/0600Z 15.1N 52.1W 50 KT 60 MPH 60H 14/1800Z 16.3N 54.6W 50 KT 60 MPH 72H 15/0600Z 17.6N 57.0W 45 KT 50 MPH 96H 16/0600Z 20.1N 61.8W 40 KT 45 MPH 120H 17/0600Z 22.9N 65.6W 35 KT 40 MPH $$ Forecaster Stewart
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