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Hurricane LESTER Forecast Discussion Number 23

2016-08-30 10:52:09| National Hurricane Center (East Pacific)

Issued at 200 AM PDT TUE AUG 30 2016 000 WTPZ43 KNHC 300852 TCDEP3 HURRICANE LESTER DISCUSSION NUMBER 23 NWS NATIONAL HURRICANE CENTER MIAMI FL EP132016 200 AM PDT TUE AUG 30 2016 Lester has begun to weaken. The areal extent of deep convection within the hurricane's central dense overcast (CDO) has decreased substantially, and the CDO has lost much of its axisymmetry since late yesterday. In addition, the eye has warmed and become a little less defined. The recent weakening could be associated with an increase in easterly shear over the cyclone as analyzed by UW-CIMSS and SHIPS model output. Dvorak T-numbers have responded by suddenly decreasing. A blend of the latest TAFB Final T- and CI-numbers, including the UW-CIMSS ADT values, is used to lower the initial intensity estimate to 110 kt. The initial motion estimate is 275/12. A strong mid-level ridge over the east-central subtropical Pacific should continue to steer Lester just north of due west for the next couple of days. A probable binary interaction with Madeline should cause Lester's heading to turn west-northwestward as the hurricane approaches the Hawaiian Islands in 3-5 days. The NHC track forecast is barely adjusted relative to the previous one, and is closest to a blend of the GFS and ECMWF solutions. The intensity forecast is, again, quite challenging. The delicate balance of environmental factors leading to Lester's annular structure yesterday may have been disrupted by the recent uptick in easterly shear. With the shear forecast to diminish over the next day or so while the cyclone continues to move over nearly constant SSTs, Lester could regain its annular characteristics. This would allow Lester to sustain a higher intensity during the next 2-3 days than what the intensity guidance indicates. After that time, the ECMWF shows a less conducive environment than the GFS, which could result in a more decided weakening. Given the greater than normal uncertainty, the NHC forecast stays close to the multi-model consensus throughout the period. Lester's wind radii have been adjusted based on a partial ASCAT overpass. FORECAST POSITIONS AND MAX WINDS INIT 30/0900Z 18.2N 133.2W 110 KT 125 MPH 12H 30/1800Z 18.3N 135.1W 100 KT 115 MPH 24H 31/0600Z 18.4N 137.5W 90 KT 105 MPH 36H 31/1800Z 18.4N 139.7W 90 KT 105 MPH 48H 01/0600Z 18.5N 141.9W 85 KT 100 MPH 72H 02/0600Z 19.3N 146.4W 80 KT 90 MPH 96H 03/0600Z 20.8N 151.2W 70 KT 80 MPH 120H 04/0600Z 22.7N 156.4W 60 KT 70 MPH $$ Forecaster Kimberlain

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Hurricane GASTON Forecast Discussion Number 31

2016-08-30 10:48:09| National Hurricane Center (Atlantic)

Issued at 500 AM AST TUE AUG 30 2016 000 WTNT42 KNHC 300848 TCDAT2 HURRICANE GASTON DISCUSSION NUMBER 31 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072016 500 AM AST TUE AUG 30 2016 Gaston is completing an eyewall replacement cycle and currently features a well-defined 35 n mi wide eye. The convective clouds have eroded somewhat west of the eye since the last advisory, and the various subjective and objective intensity estimates have also decreased. The initial intensity is thus lowered to 85 kt. The initial motion is now 055/5. A mid- to upper-level trough currently seen in water vapor images near Atlantic Canada is expected to approach Gaston during the next 12 to 24 hours, and that should cause the hurricane to become embedded in the mid-latitude westerlies. As a result, Gaston should accelerate generally east-northeastward through 72 hours. At 96 hours, a building ridge southwest of Gaston may cause a more easterly motion as the cyclone approaches the Azores Islands. This should be followed by a northeastward turn by 120 hours as a second mid-latitude trough approaches the tropical cyclone. The track guidance generally agrees with this scenario, although the model spread increases after 72 hours. The new forecast track is changed little from the previous track and lies near the center of the guidance envelope. The intensity guidance suggests that little change in strength is likely for the next 36-48 hours as Gaston moves over relatively warm water in a light or moderate westerly shear environment. After that time, increasing shear and decreasing sea surface temperatures should cause a steady decay. The new intensity forecast is an update of the previous forecast in best agreement with the SHIPS and LGEM models. FORECAST POSITIONS AND MAX WINDS INIT 30/0900Z 32.0N 54.0W 85 KT 100 MPH 12H 30/1800Z 32.4N 52.7W 85 KT 100 MPH 24H 31/0600Z 33.4N 50.6W 85 KT 100 MPH 36H 31/1800Z 35.0N 47.7W 85 KT 100 MPH 48H 01/0600Z 36.8N 43.5W 85 KT 100 MPH 72H 02/0600Z 39.5N 34.0W 70 KT 80 MPH 96H 03/0600Z 39.5N 28.5W 50 KT 60 MPH 120H 04/0600Z 42.5N 23.5W 35 KT 40 MPH $$ Forecaster Beven

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Tropical Depression NINE Forecast Discussion Number 6

2016-08-30 04:50:07| National Hurricane Center (Atlantic)

Issued at 1000 PM CDT MON AUG 29 2016 000 WTNT44 KNHC 300249 TCDAT4 TROPICAL DEPRESSION NINE DISCUSSION NUMBER 6 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092016 1000 PM CDT MON AUG 29 2016 Since the previous advisory, the depression's convective pattern has improved somewhat with the development of a cluster of deep convection with tops to -80C having developed near and also east through south of the center. Reports from nearby ships WAHV, J8NY, and C6CL6, along with reconnaissance data indicate that the low-level circulation is slowly improving. The central pressure of 1003 mb is based on a recent NOAA dropsonde report of 1005 mb with 20 kt of wind just north of the center. Since no winds of tropical storm force were sampled, the initial intensity remains at 30 kt. Similar to this time last night, the cyclone has made a jog to the west during the earlier convective hiatus period. However, the past couple of dropsonde reports suggest that the depression has resumed a longer term motion of 280/06 kt. There is little change to the previous forecast track reasoning. Other than having to adjust the forecast track southward slightly through 48 hours due to the more southerly initial position, the previous advisory track remains unchanged. The cyclone is forecast to move slowly around the western periphery of a deep-layer subtropical ridge located over southern Florida for the next 36 hours or so. By 48 hours, the depression is expected to accelerate northeastward across northern Florida ahead of a shortwave trough that is forecast to dig southeastward into the southeastern United States and northern Gulf Mexico. The new NHC track forecast lies between a blend of the GFS-ECMWF solutions and the consensus model TVCN. Data from the NOAA aircraft on its final outbound leg, along with the latest 00Z upper-air observations indicate that mid-level moisture north and northeast of the cyclone has increased since yesterday. However, water vapor imagery and upper-air data still indicate that very dry air lies just west of the cyclone across the central and western Gulf of Mexico. The global and regional models continue to indicate that some of that drier air will be entrained into the western part of the cyclone's circulation by 24-36 hours, offsetting the otherwise favorable upper-level outflow pattern and very warm SSTs of more than 30 deg C. Therefore, only gradual intensification is expected during the next 48 hours or so. When the cyclone nears the Florida Gulf coast, increasing upper-level winds are expected to limit strengthening. The official intensity forecast lies close to the previous advisory and consensus model IVCN. Given the current forecast, a tropical storm or hurricane watch may be required for a portion of the Florida Gulf coast by tomorrow morning. FORECAST POSITIONS AND MAX WINDS INIT 30/0300Z 23.9N 85.5W 30 KT 35 MPH 12H 30/1200Z 24.2N 86.4W 35 KT 40 MPH 24H 31/0000Z 24.9N 87.1W 40 KT 45 MPH 36H 31/1200Z 25.8N 87.0W 45 KT 50 MPH 48H 01/0000Z 27.2N 85.8W 55 KT 65 MPH 72H 02/0000Z 30.1N 82.2W 50 KT 60 MPH...INLAND 96H 03/0000Z 33.1N 75.5W 50 KT 60 MPH...OVER WATER 120H 04/0000Z 35.8N 68.7W 50 KT 60 MPH $$ Forecaster Stewart

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Hurricane LESTER Forecast Discussion Number 22

2016-08-30 04:36:38| National Hurricane Center (East Pacific)

Issued at 800 PM PDT MON AUG 29 2016 000 WTPZ43 KNHC 300236 TCDEP3 HURRICANE LESTER DISCUSSION NUMBER 22 NWS NATIONAL HURRICANE CENTER MIAMI FL EP132016 800 PM PDT MON AUG 29 2016 Lester is a powerful category 4 hurricane. The eye of the hurricane, which is now about 20 n mi wide, has expanded and cleared out during the last several hours. Visible satellite images also indicate that mesovorticies exist within the eye. The convective pattern has been very symmetric, and the hurricane continues to have an annular appearance in satellite images. The latest Dvorak classifications from TAFB and SAB were 6.5/127 kt and 5.5/102 kt, respectively. Based on these estimates and automated Dvorak values from CIMSS at the University of Wisconsin, the initial wind speed is raised a little to 120 kt. Lester is estimated to have strengthened at an impressive rate of 45 kt during the past 24 hours. The major hurricane is likely near its peak intensity, but fluctuations in strength are possible in the short term. Beyond that time, marginally warm sea surface temperatures and a stable air mass suggest that Lester will likely weaken gradually during the next several days. The NHC intensity forecast is similar to the previous one and is fairly close to the intensity model consensus. Lester continues to move due westward about 12 kt on the south side of a strong mid-level high pressure system. A continued westward track at about the same forward speed is predicted during the next few days while the system remains to the south of the ridge. After that time, a slight turn toward the west-northwest is likely due to some interaction with another tropical cyclone, Madeline, to its west-southwest. The models remain tightly clustered, and the NHC official track forecast lies near the middle of the guidance envelope. This forecast takes Lester close to the Hawaiian Islands in about 5 days. FORECAST POSITIONS AND MAX WINDS INIT 30/0300Z 18.1N 131.8W 120 KT 140 MPH 12H 30/1200Z 18.2N 133.7W 115 KT 130 MPH 24H 31/0000Z 18.2N 136.0W 105 KT 120 MPH 36H 31/1200Z 18.3N 138.3W 95 KT 110 MPH 48H 01/0000Z 18.3N 140.5W 90 KT 105 MPH 72H 02/0000Z 19.0N 145.0W 85 KT 100 MPH 96H 03/0000Z 20.3N 149.9W 80 KT 90 MPH 120H 04/0000Z 22.0N 154.8W 70 KT 80 MPH $$ Forecaster Cangialosi

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Hurricane GASTON Forecast Discussion Number 30

2016-08-30 04:34:38| National Hurricane Center (Atlantic)

Issued at 1100 PM AST MON AUG 29 2016 000 WTNT42 KNHC 300234 TCDAT2 HURRICANE GASTON DISCUSSION NUMBER 30 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072016 1100 PM AST MON AUG 29 2016 The satellite presentation of Gaston has not changed much during the last several hours. The eye is ragged-looking in infrared satellite images and recent microwave data indicate that there are some signs of a double eyewall structure. The initial intensity is held at 90 kt for this advisory, in agreement with the Dvorak CI-numbers from TAFB and SAB. Gaston will likely change little in strength during the next couple of days while it remains in generally conducive environmental conditions. However, fluctuations in strength are possible if the cyclone continues to undergo an eyewall replacement. Beyond a couple of days, steady weakening is anticipated when the hurricane moves over cooler waters and into an environment of increasing shear and drier air. The NHC intensity forecast is largely unchanged from the previous one. Gaston has turned northeastward and is moving a bit faster, with the initial motion estimated to be 045/5 kt. A trough currently seen in water vapor images near Atlantic Canada is expected to approach Gaston during the next 12 to 24 hours, and that should cause the hurricane to become embedded in the mid-latitude westerlies. This should result in Gaston turning east-northeastward on Tuesday with a steady increase in forward speed during the next few days. The model guidance has shifted a little to the north this cycle, and the NHC track forecast has been nudged in that direction. FORECAST POSITIONS AND MAX WINDS INIT 30/0300Z 31.6N 54.6W 90 KT 105 MPH 12H 30/1200Z 32.1N 53.6W 85 KT 100 MPH 24H 31/0000Z 32.8N 51.7W 85 KT 100 MPH 36H 31/1200Z 34.0N 49.4W 85 KT 100 MPH 48H 01/0000Z 35.7N 45.9W 85 KT 100 MPH 72H 02/0000Z 39.0N 36.3W 70 KT 80 MPH 96H 03/0000Z 40.0N 29.2W 50 KT 60 MPH 120H 04/0000Z 41.0N 24.8W 40 KT 45 MPH $$ Forecaster Cangialosi

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