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Tropical Storm HERNAN Forecast Discussion Number 11

2014-07-28 22:32:35| National Hurricane Center (East Pacific)

Issued at 200 PM PDT MON JUL 28 2014 000 WTPZ43 KNHC 282032 TCDEP3 TROPICAL STORM HERNAN DISCUSSION NUMBER 11 NWS NATIONAL HURRICANE CENTER MIAMI FL EP082014 200 PM PDT MON JUL 28 2014 The cloud pattern of Hernan continues to degrade in appearance, and what little deep convection remains is confined mainly to the south of the center. The current wind speed estimate has been reduced to 45 kt based on a blend of intensity estimates from SAB and TAFB along with objective Dvorak numbers from UW-CIMSS. The storm is now moving over waters cooler than 26 deg C, and sea surface temperatures should continue to decrease beneath the cyclone. These hostile oceanic conditions, combined with moderately strong south-southwesterly shear, are likely to bring about continued weakening. The official intensity forecast shows Hernan degenerating into a remnant low in 36 hours, but the latest intensity model guidance suggests that the system could weaken even faster than indicated here. Hernan continues on its west-northwestward trek, and the initial motion is estimated to be 300/15 kt. A mid-level ridge over the southwestern United States and northwestern Mexico should impart a continued west-northwestward motion for the next couple of days. Thereafter, the dying cyclone is expected to turn westward since the steering should become dominated by the low-level tradewind flow. The official track forecast is quite similar to the previous NHC track and is very close to the latest dynamical model consensus forecast, TVCE. FORECAST POSITIONS AND MAX WINDS INIT 28/2100Z 21.3N 117.3W 45 KT 50 MPH 12H 29/0600Z 22.4N 119.3W 40 KT 45 MPH 24H 29/1800Z 23.6N 121.5W 30 KT 35 MPH 36H 30/0600Z 24.2N 123.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 30/1800Z 24.5N 124.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 31/1800Z 24.5N 126.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 01/1800Z...DISSIPATED $$ Forecaster Pasch

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Tropical Storm HERNAN Forecast Discussion Number 10

2014-07-28 16:38:02| National Hurricane Center (East Pacific)

Issued at 800 AM PDT MON JUL 28 2014 000 WTPZ43 KNHC 281437 TCDEP3 TROPICAL STORM HERNAN DISCUSSION NUMBER 10 NWS NATIONAL HURRICANE CENTER MIAMI FL EP082014 800 AM PDT MON JUL 28 2014 Persistent 15-20 kt of westerly shear is certainly deteriorating the cyclone's organization this morning. Conventional satellite imagery shows a rather shapeless cloud pattern with warming cloud tops. A fortuitous 0934 UTC AMSU-A microwave pass indicated an eastward vertical tilt with the low-level center located near the western edge of the deep convection. A compromise of satellite intensity estimates from TAFB and SAB along with a 0933 UTC UW-CIMSS SATCON (which includes ADT, and AMSU intensity estimates) of 54 kt supports an initial intensity of 55 kt for this advisory. The large-scale models and the statistical/dynamical intensity guidance all show a moderate shear environment through the forecast period. Furthermore, an increasingly stable air mass and decreasing sea surface temperatures should ultimately weaken Hernan into a shallow post-tropical cyclone in 48 hours. Hernan continues to move northwestward, with an initial motion estimate of 295/14 kt. Global model guidance indicates that a mid-level ridge to the northeast of the cyclone should steer Hernan in this general motion through the 36 hour period. Afterward, a turn toward the west and a reduction in forward speed is forecast as the remnant low moves within the lower tropospheric flow of the subtropical ridge. The NHC forecast is again adjusted slightly to the left of the previous track beyond 36 hours, and lies between the consensus model and the ECMWF. FORECAST POSITIONS AND MAX WINDS INIT 28/1500Z 20.5N 115.9W 55 KT 65 MPH 12H 29/0000Z 21.6N 117.8W 50 KT 60 MPH 24H 29/1200Z 22.9N 120.3W 40 KT 45 MPH 36H 30/0000Z 23.8N 122.2W 30 KT 35 MPH 48H 30/1200Z 24.0N 123.4W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 31/1200Z 24.0N 125.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 01/1200Z 24.0N 127.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 02/1200Z...DISSIPATED $$ Forecaster Roberts

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Tropical Storm HERNAN Forecast Discussion Number 9

2014-07-28 10:38:31| National Hurricane Center (East Pacific)

Issued at 200 AM PDT MON JUL 28 2014 000 WTPZ43 KNHC 280838 TCDEP3 TROPICAL STORM HERNAN DISCUSSION NUMBER 9 NWS NATIONAL HURRICANE CENTER MIAMI FL EP082014 200 AM PDT MON JUL 28 2014 Hernan is now on a weakening trend. The coverage of deep convection has decreased markedly over the past several hours, and the cloud pattern has a more elongated appearance than it did earlier. Microwave images also show a pronounced vertical tilt of the vortex due to about 15 kt of westerly shear. Dvorak and ADT intensity estimates have decreased from all agencies, and using a blend of the CI- and T-numbers yields an initial intensity of 60 kt. A combination of moderate shear, a dry stable air mass, and decreasing sea surface temperatures should cause Hernan to continue weakening during the next few days. The system is expected to become a remnant low in about 2 days when it is forecast to be over waters cooler than 23 C. The storm has turned slightly to the left, and the latest initial motion estimate is 300/13 kt. This general motion should continue for the next 24 hours while Hernan remains steered by a strong mid-level high over the southwestern United States. After that time, a gradual turn to the west with a decrease in forward speed is predicted when the shallow system becomes more influenced by the lighter low-level flow. The official track forecast is just a little to the left of the previous one, and near the multi-model consensus TVCE. FORECAST POSITIONS AND MAX WINDS INIT 28/0900Z 19.9N 114.5W 60 KT 70 MPH 12H 28/1800Z 20.9N 116.4W 50 KT 60 MPH 24H 29/0600Z 22.3N 118.8W 45 KT 50 MPH 36H 29/1800Z 23.4N 120.6W 35 KT 40 MPH 48H 30/0600Z 24.1N 122.2W 30 KT 35 MPH...POST-TROP/REMNT LOW 72H 31/0600Z 24.5N 124.2W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 01/0600Z 24.5N 126.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 02/0600Z...DISSIPATED $$ Forecaster Cangialosi

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Hurricane HERNAN Forecast Discussion Number 8

2014-07-28 04:40:14| National Hurricane Center (East Pacific)

Issued at 800 PM PDT SUN JUL 27 2014 000 WTPZ43 KNHC 280240 TCDEP3 HURRICANE HERNAN DISCUSSION NUMBER 8 NWS NATIONAL HURRICANE CENTER MIAMI FL EP082014 800 PM PDT SUN JUL 27 2014 Hernan's cloud pattern has already begun to deteriorate a bit since it reached hurricane strength this afternoon. The last few visible images showed arc clouds emanating away from the western semicircle, which could be an indication that drier air is getting into the circulation. Satellite intensity estimates are somewhat conflicting, with the subjective numbers from TAFB and SAB increasing from 6 hours ago while the objective T-numbers from the ADT have decreased. Therefore, the intensity is being held at 65 kt for this advisory. Given the recent satellite trends, however, Hernan may not last as a hurricane for much longer. The cyclone only has about 12-18 hours left before it crosses the 26C isotherm and plows over much colder water, leading to a quicker weakening trend after 24 hours. The main difference with the previous forecast is at 48 hours and beyond, with Hernan now expected to become a remnant low by day 3 and dissipate by day 5. Hernan continues to move northwestward with an initial motion of 310/13 kt. This motion is being caused by a strong mid-level ridge located over Mexico and the southern United States and should continue for the next 36 hours. After that time, the cyclone is forecast to turn west-northwestward and slow down considerably as it is left in an environment of weak low-level steering. The updated NHC forecast is nudged a bit north of the previous forecast beyond 48 hours toward the model consensus TVCE. FORECAST POSITIONS AND MAX WINDS INIT 28/0300Z 19.3N 113.1W 65 KT 75 MPH 12H 28/1200Z 20.3N 114.9W 60 KT 70 MPH 24H 29/0000Z 21.8N 117.3W 55 KT 65 MPH 36H 29/1200Z 23.1N 119.5W 50 KT 60 MPH 48H 30/0000Z 23.9N 121.1W 40 KT 45 MPH 72H 31/0000Z 24.5N 123.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 01/0000Z 24.5N 125.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 02/0000Z...DISSIPATED $$ Forecaster Berg

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Hurricane HERNAN Forecast Discussion Number 7

2014-07-27 22:32:27| National Hurricane Center (East Pacific)

Issued at 200 PM PDT SUN JUL 27 2014 000 WTPZ43 KNHC 272031 TCDEP3 HURRICANE HERNAN DISCUSSION NUMBER 7 NWS NATIONAL HURRICANE CENTER MIAMI FL EP082014 200 PM PDT SUN JUL 27 2014 A faint eye was briefly apparent on visible satellite images, and Dvorak classifications from TAFB as well as objective Dvorak intensity estimates from UW-CIMSS support an intensity of 65 kt. Therefore, Hernan is being upgraded to the third hurricane of the 2014 eastern North Pacific season. The system has a quite impressive and symmetrical upper-level outflow pattern at this time. Sea surface temperatures will be decreasing along the path of the tropical cyclone, and vertical shear is expected to gradually increase. Therefore, a weakening trend should commence on Monday. The official intensity forecast closely follows the latest model consensus, ICON. The initial motion remains northwestward, or 305/13. There is no significant change to the track forecast or the reasoning behind it. For the next few days, Hernan will continue to be steered by the flow on the southwest side of a ridge associated with a mid-tropospheric high centered over the southwestern United States. This ridge is forecast to build westward somewhat, which should cause the track of Hernan to gradually shift toward the west-northwest. By the latter part of the forecast period, the weakening and increasingly shallow cyclone is likely to turn westward following the lower-tropospheric steering flow. The official track forecast is very close to the track model consensus, TVCN, and is basically an update of the previous NHC forecast. Based on a recent ASCAT overpass, only slight adjustments to the wind radii were required. FORECAST POSITIONS AND MAX WINDS INIT 27/2100Z 18.6N 112.2W 65 KT 75 MPH 12H 28/0600Z 19.7N 113.9W 65 KT 75 MPH 24H 28/1800Z 21.2N 116.3W 60 KT 70 MPH 36H 29/0600Z 22.6N 118.7W 50 KT 60 MPH 48H 29/1800Z 23.4N 120.6W 45 KT 50 MPH 72H 30/1800Z 24.2N 124.0W 30 KT 35 MPH 96H 31/1800Z 24.5N 127.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 01/1800Z 24.5N 129.5W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Pasch

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