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Hurricane FERNANDA Forecast Discussion Number 16

2017-07-15 22:34:58| National Hurricane Center (East Pacific)

Issued at 200 PM PDT Sat Jul 15 2017 000 WTPZ41 KNHC 152034 TCDEP1 Hurricane Fernanda Discussion Number 16 NWS National Hurricane Center Miami FL EP062017 200 PM PDT Sat Jul 15 2017 A recent AMSU pass indicates that Fernanda continues to have a double eyewall structure, with the inner eye about 20 n mi in diameter and the outer eye about 60 n mi across. The appearance of Fernanda in geostationary satellite images remains impressive with a small distinct eye surrounding by a ring of cold cloud tops. The cold cloud tops, however, are not quite as expansive as they were earlier. Accordingly, the latest satellite intensity estimates have decreased slightly and range from 105 to 125 kt, and based on these data, the initial wind speed is lowered a little to 115 kt. It should be noted that it is common for hurricanes that undergo eyewall replacement cycles (ERC) to weaken during the beginning of the process. Assuming the ERC completes, Fernanda has an opportunity to restrengthen during the next day or so while it remains in favorable atmospheric conditions and over warm water. After that time, steady, or even rapid, weakening is expected as the hurricane moves over cooler water and into a drier and more stable air mass. An increase in southwesterly shear should aid in the weakening process toward the end of the forecast period. The NHC intensity forecast is at the high end, or slightly above, the guidance in the short term, but then falls in line with the intensity model consensus after that. This forecast is a tad lower than the previous one. A mid-level ridge located over the western United States is steering Fernanda westward, or 280 degrees, at 11 kt. A west-northwestward motion is expected to begin tonight and continue for the next several days while the hurricane moves toward a weakness at the western periphery of the ridge. The track models remain in good agreement, and the NHC track forecast lies near the middle of the guidance envelope, in best agreement with the various consensus models. FORECAST POSITIONS AND MAX WINDS INIT 15/2100Z 11.4N 124.0W 115 KT 130 MPH 12H 16/0600Z 11.9N 125.8W 125 KT 145 MPH 24H 16/1800Z 12.7N 128.2W 125 KT 145 MPH 36H 17/0600Z 13.4N 130.4W 120 KT 140 MPH 48H 17/1800Z 14.1N 132.3W 105 KT 120 MPH 72H 18/1800Z 15.7N 135.5W 80 KT 90 MPH 96H 19/1800Z 16.8N 138.3W 60 KT 70 MPH 120H 20/1800Z 17.3N 141.6W 50 KT 60 MPH $$ Forecaster Cangialosi

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Hurricane Fernanda Forecast Discussion Number 15

2017-07-15 16:34:33| National Hurricane Center (East Pacific)

Issued at 800 AM PDT Sat Jul 15 2017 000 WTPZ41 KNHC 151434 TCDEP1 Hurricane Fernanda Discussion Number 15 NWS National Hurricane Center Miami FL EP062017 800 AM PDT Sat Jul 15 2017 An AMSR2 overpass around 0925 UTC shows that Fernanda is undergoing an eyewall replacement cycle (ERC). Based on the 36 GHz composite image from that pass, the inner core at that time consisted of a very small, 10 nm-wide, inner eyewall surrounded by a 30 nm-wide outer eyewall. An earlier WindSat pass at 0149 UTC suggests that the ERC began about 12 hours ago. This is consistent with a warming trend observed in the cloud top temperatures that began a little before 0000 UTC yesterday. The initial intensity has been decreased to 120 kt, based on a blend of Dvorak estimates from TAFB, SAB, and the UW-CIMSS ADT. Assuming a typical ERC weakening period of about 15 hours, the hurricane could reintensify later today, once the outer eyewall contracts. The environment should support intensification for another 24 hours or so, and the forecast reflects this. Additional ERCs could lead to fluctuations in intensity that aren't explicitly shown in the forecast. After about 36 hours, the hurricane will become embedded in a drier and more stable environment, so steady weakening is anticipated. The new forecast is similar to the previous one, despite the weaker initial intensity, and is above most of the intensity guidance for the first 36 hours. It is close to the intensity consensus by the end of the forecast period. Fernanda is beginning to make a long-anticipated turn toward the west-northwest and the initial motion is now just north of due west, or 275/11. Almost no change has been made to the track forecast, which remains on top of the various multi-model consensus aids. A west-northwest to northwest motion is expected for the next several days while the cyclone moves along the southwestern periphery of a deep-layer ridge. The track guidance is still tightly clustered, and confidence remains high in the track forecast. FORECAST POSITIONS AND MAX WINDS INIT 15/1500Z 11.0N 123.0W 120 KT 140 MPH 12H 16/0000Z 11.5N 124.8W 130 KT 150 MPH 24H 16/1200Z 12.3N 127.3W 130 KT 150 MPH 36H 17/0000Z 13.0N 129.7W 125 KT 145 MPH 48H 17/1200Z 13.8N 131.9W 120 KT 140 MPH 72H 18/1200Z 15.3N 135.3W 95 KT 110 MPH 96H 19/1200Z 16.5N 138.0W 70 KT 80 MPH 120H 20/1200Z 17.0N 141.0W 50 KT 60 MPH $$ Forecaster Zelinsky

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Hurricane Fernanda Forecast Discussion Number 14

2017-07-15 10:34:47| National Hurricane Center (East Pacific)

Issued at 200 AM PDT Sat Jul 15 2017 000 WTPZ41 KNHC 150834 TCDEP1 Hurricane Fernanda Discussion Number 14 NWS National Hurricane Center Miami FL EP062017 200 AM PDT Sat Jul 15 2017 Fernanda has not intensified during the past few hours. The convective tops surrounding the eye have warmed up a little, but the overall cloud pattern continues to be very impressive. The Dvorak T-numbers are 6.0 and 6.5 indicating that winds are still around 125 kt. Fernanda has the possibility of some strengthening during the next 12 to 24 hours since the hurricane is embedded within light shear and moving over warm waters. After that time, the hurricane will likely maintain the same intensity for a couple of days, but a weakening trend should then begin as the circulation of the cyclone encounters cooler waters by the end of the forecast period. The NHC forecast continues to be above the intensity guidance, and does not vary much from the previous one. The hurricane is moving toward the west or 270 degrees at 10 kt. The cyclone is being steered by a deep layer of easterlies associated with a strong subtropical ridge. A general westward track with a gradual turn to the west-northwest is anticipated as the hurricane approaches the western portion of the ridge over the next 5 days. Track guidance is tightly clustered, and the NHC forecast is basically on top of the multi-model consensus. FORECAST POSITIONS AND MAX WINDS INIT 15/0900Z 10.8N 121.8W 125 KT 145 MPH 12H 15/1800Z 11.1N 123.6W 135 KT 155 MPH 24H 16/0600Z 11.8N 125.9W 130 KT 150 MPH 36H 16/1800Z 12.5N 128.5W 130 KT 150 MPH 48H 17/0600Z 13.5N 131.0W 125 KT 145 MPH 72H 18/0600Z 15.0N 135.0W 105 KT 120 MPH 96H 19/0600Z 16.5N 138.0W 80 KT 90 MPH 120H 20/0600Z 17.0N 140.5W 60 KT 70 MPH $$ Forecaster Avila

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Hurricane Fernanda Forecast Discussion Number 12

2017-07-14 22:33:46| National Hurricane Center (East Pacific)

Issued at 200 PM PDT Fri Jul 14 2017 000 WTPZ41 KNHC 142033 TCDEP1 Hurricane Fernanda Discussion Number 12 NWS National Hurricane Center Miami FL EP062017 200 PM PDT Fri Jul 14 2017 Fernanda's satellite presentation has become even more impressive than earlier today, with the eye becoming more distinct on geostationary and microwave imagery. The upper-level outflow is well-defined over all quadrants, with a fairly symmetric CDO. There are also banding features over the eastern semicircle of the circulation. Subjective and objective Dvorak T-numbers are near 6.0 corresponding to an intensity of 115 kt, and that value will be used for the advisory intensity. It may be of interest that it is quite unusual to have a hurricane this strong so far south in the eastern North Pacific basin. Fernanda will remain in a low-shear environment for the next few days, with high oceanic heat content. Based on the trends over the past 24 hours, the official intensity forecast is above most of the numerical guidance. One complication to the forecast is the possibility of an eyewall replacement cycle, which is not accounted for here. Late in the forecast period somewhat cooler waters and, by day 5, some increase in shear should cause weakening. The initial motion remains near 265/10 kt. There has not been much change in the track forecast reasoning from the previous couple of advisories. A mid-level subtropical ridge to the north of Fernanda should induce a westward to west-northwestward track for the next several days. Some decrease in forward speed is likely later in the period when the tropical cyclone nears a weakness or col region of the ridge. The official track forecast is a blend of the simple and corrected dynamical consensus predictions. FORECAST POSITIONS AND MAX WINDS INIT 14/2100Z 10.7N 119.7W 115 KT 130 MPH 12H 15/0600Z 10.9N 121.4W 125 KT 145 MPH 24H 15/1800Z 11.3N 123.7W 130 KT 150 MPH 36H 16/0600Z 11.9N 126.1W 130 KT 150 MPH 48H 16/1800Z 12.5N 128.4W 125 KT 145 MPH 72H 17/1800Z 13.9N 132.5W 110 KT 125 MPH 96H 18/1800Z 15.4N 136.0W 90 KT 105 MPH 120H 19/1800Z 16.5N 139.0W 70 KT 80 MPH $$ Forecaster Pasch

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Hurricane Fernanda Forecast Discussion Number 11

2017-07-14 16:36:46| National Hurricane Center (East Pacific)

Issued at 800 AM PDT Fri Jul 14 2017 000 WTPZ41 KNHC 141436 TCDEP1 Hurricane Fernanda Discussion Number 11 NWS National Hurricane Center Miami FL EP062017 800 AM PDT Fri Jul 14 2017 The satellite presentation of Fernanda continues to improve. An eye has been apparent in shortwave and longwave IR imagery for the past several hours. An AMSR-2 overpass around 0843 UTC showed a well defined eye structure, completely surrounded by deep convection. Subjective Dvorak T-numbers at 1200 UTC increased to 5.0 from TAFB and 5.5 from SAB, and since that time the cloud top structure has improved a little more. On that basis, the initial intensity has been increased to 100 kt, making Fernanda the second major hurricane of the 2017 eastern North Pacific hurricane season. Fernanda remains in a very favorable environment for intensification. The cyclone's intensity has increased by 40 kt in the past 24 hours and there are no current indications that the period of rapid intensification has ended. In fact, according to the SHIPS diagnostics, the hurricane is now approaching an area of higher ocean heat content. Surprisingly, most of the guidance shows relatively little increase in intensity during the next 48 hours. Considering that most of the guidance has thus far shown not nearly the extent of intensification that has been observed, the NHC forecast remains well above the guidance. The NHC forecast has been adjusted substantially higher for the first 36 hours to account for the higher initial intensity, but is closer to the previous forecast after that. Beyond 48 hours, lower SSTs along the forecast track and a drier environment should lead to a gradual weakening. The hurricane is continuing its steady westward track and the initial motion estimate is 265/10 kt. There is no change to the track forecast reasoning, and confidence in the track forecast remains high due to a tight clustering of the model tracks. Fernanda is still expected to move generally westward for the next day or so, before turning toward the west-northwest due to a weakening of the ridge to the north. No significant changes were made to the NHC track forecast, which remains very close to the various multi-model consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 14/1500Z 10.9N 118.9W 100 KT 115 MPH 12H 15/0000Z 10.9N 120.3W 110 KT 125 MPH 24H 15/1200Z 11.3N 122.5W 120 KT 140 MPH 36H 16/0000Z 11.8N 124.9W 125 KT 145 MPH 48H 16/1200Z 12.5N 127.3W 125 KT 145 MPH 72H 17/1200Z 13.8N 131.8W 115 KT 130 MPH 96H 18/1200Z 15.0N 135.2W 95 KT 110 MPH 120H 19/1200Z 16.3N 138.6W 75 KT 85 MPH $$ Forecaster Zelinsky

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