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Hurricane Otis Forecast Discussion Number 25

2017-09-17 22:51:38| National Hurricane Center (East Pacific)

Issued at 200 PM PDT Sun Sep 17 2017 000 WTPZ45 KNHC 172051 TCDEP5 Hurricane Otis Discussion Number 25 NWS National Hurricane Center Miami FL EP152017 200 PM PDT Sun Sep 17 2017 Otis continues to surprise us. Satellite images indicate that the eye has become more distinct during the past few hours, and the deep convection is wrapping around that center. The cyclone is currently undergoing rapid intensification, and the initial intensity is increased significantly to 90 kt based on a blend of the latest satellite estimates. This makes Otis a category 2 hurricane on the Saffir-Simpson Hurricane Wind Scale. Even though Otis is a powerful cyclone, recent ASCAT data confirms that the wind field of the system is extremely compact. Some additional strengthening is likely during the next 12 hours or so while the hurricane remains in an environment of low wind shear and over 27 deg C waters. After that time, however, lower SSTs, drier air, and an increase in wind shear should cause rapid weakening. Even though Otis will be moving over warmer waters by the end of the forecast period, the models continue to show Otis decaying due to unfavorable atmospheric conditions. The cyclone is still forecast to become a remnant low by day 4 based on the global models, but this is a low confidence prediction at this time. The hurricane continues to move slowly northward at 4 kt. A slow north to north-northwest motion is expected during the next 24 to 36 hours while Otis moves on the west side of a weak mid-level ridge. Thereafter, a faster west and west-southwest motion is expected when the weakening cyclone becomes more influenced by the low-level tradewind flow. This track forecast is not too different from the previous one, and it lies close to the various consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 17/2100Z 17.0N 127.3W 90 KT 105 MPH 12H 18/0600Z 17.7N 127.4W 110 KT 125 MPH 24H 18/1800Z 18.6N 127.6W 90 KT 105 MPH 36H 19/0600Z 19.0N 128.0W 70 KT 80 MPH 48H 19/1800Z 18.8N 128.6W 50 KT 60 MPH 72H 20/1800Z 17.7N 130.7W 35 KT 40 MPH 96H 21/1800Z 16.4N 133.7W 30 KT 35 MPH...POST-TROP/REMNT LOW 120H 22/1800Z 15.0N 136.5W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Cangialosi

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Tropical Depression Lee Forecast Discussion Number 12

2017-09-17 22:49:36| National Hurricane Center (Atlantic)

Issued at 500 PM AST Sun Sep 17 2017 000 WTNT44 KNHC 172049 TCDAT4 Tropical Depression Lee Discussion Number 12 NWS National Hurricane Center Miami FL AL142017 500 PM AST Sun Sep 17 2017 A small burst of deep convection re-formed near Lee's center, but since the earlier ASCAT pass barely showed 30 kt, that will remain the initial intensity. Increasing shear and a dry mid-level environment will continue to take a toll on Lee during the next few days. Gradual weakening is still expected, and Lee could lose organized deep convection by 36 hours, if not sooner. The GFS and ECMWF models degenerate the system into a surface trough by day 3, and dissipation is now indicated in the NHC forecast at that time. Lee is moving westward, or 280/7 kt, but it should turn west-northwestward soon due to the weakness of the subtropical ridge to its north. A west-northwestward or northwestward motion should continue until Lee dissipates on day 3. Little change was required to the updated NHC track forecast, which lies close to the consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 17/2100Z 13.2N 37.3W 30 KT 35 MPH 12H 18/0600Z 13.5N 38.6W 25 KT 30 MPH 24H 18/1800Z 14.3N 40.3W 25 KT 30 MPH 36H 19/0600Z 15.4N 41.9W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 19/1800Z 16.6N 43.3W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 20/1800Z...DISSIPATED $$ Forecaster Berg

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Tropical Storm Maria Forecast Discussion Number 5

2017-09-17 16:53:02| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Sun Sep 17 2017 000 WTNT45 KNHC 171452 TCDAT5 Tropical Storm Maria Discussion Number 5 NWS National Hurricane Center Miami FL AL152017 1100 AM AST Sun Sep 17 2017 The cloud pattern has not changed much since the last advisory. There appears to be a dry slot working into the western side of Maria, and the low-level circulation seems to be peaking out from under the western side of a persistent CDO feature. Dvorak estimates are unchanged from six hours ago, so the initial intensity is held at 55 kt. An Air Force Reserve Hurricane Hunter aircraft will be investigating Maria this afternoon. Maria continues to move west-northwestward, or 290/13 kt, and that trajectory is expected to continue at least for the next four days while a mid-level high is centered over the western Atlantic Ocean. However, the track guidance has generally slowed down since the high is not very expansive or strong, and the new NHC track forecast follows that trend, ending up a little slower than the previous forecast. The official forecast also continues to hedge toward the southern side of the track guidance envelope, closest to the ECMWF and HCCA models, which have been doing very well this hurricane season. Until the reconnaissance aircraft investigates Maria, the initial intensity will be a little uncertain. Regardless, the storm is within an environment of very low shear and over sea surface temperatures around 29 degrees Celsius, so steady strengthening is expected during the next few days. Due to this seemingly ideal environment, the NHC intensity forecast is higher than the statistical-dynamical guidance and closely follows HCCA and the ICON intensity consensus through the entire forecast period. Maria is likely to become a hurricane later today and could become a major hurricane in 2 to 3 days. No major changes to the intensity forecast were necessary compared with the previous cycle, and I'd rather wait anyway until we have a better handle on Maria's intensity and structure. KEY MESSAGES: 1. Maria is expected to strengthen and affect portions of the Leeward Islands as a hurricane early this week, bringing dangerous wind, storm surge and rainfall hazards. Hurricane and tropical storm warnings have been issued for portions of the Leeward Islands, and these warnings will likely be extended northward and westward later today and tonight. 2. Maria could also affect the British and U.S. Virgin Islands and Puerto Rico by mid week as a dangerous major hurricane, and hurricane watches could be issued for these islands as early as tonight. Interests in these areas should monitor the progress of Maria and follow any advice given by local officials. FORECAST POSITIONS AND MAX WINDS INIT 17/1500Z 13.5N 56.2W 55 KT 65 MPH 12H 18/0000Z 14.1N 57.7W 65 KT 75 MPH 24H 18/1200Z 14.8N 59.3W 75 KT 85 MPH 36H 19/0000Z 15.5N 60.7W 85 KT 100 MPH 48H 19/1200Z 16.1N 62.0W 95 KT 110 MPH 72H 20/1200Z 17.3N 64.7W 110 KT 125 MPH 96H 21/1200Z 18.5N 67.5W 105 KT 120 MPH 120H 22/1200Z 20.0N 69.5W 100 KT 115 MPH $$ Forecaster Berg

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Tropical Storm Otis Forecast Discussion Number 24

2017-09-17 16:53:02| National Hurricane Center (East Pacific)

Issued at 800 AM PDT Sun Sep 17 2017 000 WTPZ45 KNHC 171452 TCDEP5 Tropical Storm Otis Discussion Number 24 NWS National Hurricane Center Miami FL EP152017 800 AM PDT Sun Sep 17 2017 Otis continues to gradually strengthen. Satellite images show hints of an eye starting to form, and convection just outside the center has been increasing during the past few hours. A blend of the TAFB Dvorak classification and ADT values from CIMSS at the University of Wisconsin supports increasing the winds to 50 kt, though this could be conservative based on the current structure. Otis has a little more time to strengthen since the storm is expected to remain in an environment of low wind shear and over 27 deg C waters. After 24 hours, however, lower SSTs, drier air, and an increase in wind shear should cause weakening. Even though SSTs warm along the expected path by the end of the forecast period, the models continue to show Otis decaying due to unfavorable atmospheric conditions. The cyclone is forecast to become a remnant low by day 4 based on the global models, but this is a low confidence prediction at this time. The tropical storm has now turned to the north, as expected, at a very slow forward speed. This slow north to north-northwest motion is expected during the next 36 hours while Otis moves on the west side of a weak mid-level ridge. Thereafter, a faster west and west-southwest motion is expected when the weakening cyclone becomes more influenced by the low-level tradewind flow. Only minor changes were made to the previous NHC track forecast, and this one lies close to the various consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 17/1500Z 16.3N 127.3W 50 KT 60 MPH 12H 18/0000Z 17.1N 127.4W 55 KT 65 MPH 24H 18/1200Z 18.0N 127.5W 55 KT 65 MPH 36H 19/0000Z 18.8N 127.7W 50 KT 60 MPH 48H 19/1200Z 18.9N 128.3W 45 KT 50 MPH 72H 20/1200Z 18.1N 130.1W 35 KT 40 MPH 96H 21/1200Z 17.0N 133.1W 30 KT 35 MPH...POST-TROP/REMNT LOW 120H 22/1200Z 15.7N 136.6W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Cangialosi

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Hurricane Jose Forecast Discussion Number 49

2017-09-17 16:50:00| National Hurricane Center (Atlantic)

Issued at 1100 AM EDT Sun Sep 17 2017 000 WTNT42 KNHC 171449 TCDAT2 Hurricane Jose Discussion Number 49 NWS National Hurricane Center Miami FL AL122017 1100 AM EDT Sun Sep 17 2017 The Air Force Hurricane Hunters have been investigating Jose this morning and found flight-level winds of 86 kt, SFMR surface winds of 89 kt, and a minimum pressure of 967 mb. Based on these data, the initial wind speed is raised to 80 kt for this advisory. Even though the winds are stronger than earlier, the hurricane does not have an improved appearance in satellite images. In fact, the Air Force meteorologist onboard the aircraft mentioned that the inner core of Jose is asymmetric and the overall appearance is lopsided. Jose is expected to be in an environment of strong southwesterly wind shear while it is over the warm Gulf Stream waters during the next couple of days. Although the shear is forecast to lessen beyond that time, the hurricane will likely have crossed the north wall of the Gulf Stream by then, where the waters are much cooler. These environmental conditions favor a slow weakening trend during the next several days, and that is reflected in the NHC intensity forecast. It should be noted, however, that despite the expected weakening, the models suggest that Jose's outer wind field will expand, which is typical for tropical cyclones that move into the mid-latitudes. The hurricane is moving northward at 8 kt on the west side of a subtropical ridge. This motion is expected to continue for 2 to 3 days while the steering pattern persists. Thereafter, a trough currently over central Canada is expected to move eastward and should cause Jose to turn to the northeast and east at a slow forward speed in the 3- to 5-day time frame. The NHC track forecast has been shifted slightly to the left of the previous one, mainly because of the more westward initial position. KEY MESSAGES: 1. The center of Jose is forecast to pass well east of the North Carolina coast on Monday, and tropical-storm-force winds are currently expected to remain offshore of the North Carolina Outer Banks. However, an additional increase in the size of the storm or a westward adjustment in the track forecast could bring tropical storm conditions closer to the Outer Banks, and interests there should monitor the progress of Jose through Monday. 2. While the center of Jose is currently forecast to remain offshore of the U.S. coast, the large cyclone could cause some direct impacts from Virginia northward to New England, and any deviation to the left of the NHC forecast track would increase the likelihood and magnitude of those impacts. Interests along the U.S. east coast from Virginia to New England should monitor the progress of Jose through the next several days. Tropical storm watches could be required for a portion of this area later today. 3. Swells generated by Jose are affecting Bermuda, the Bahamas, and much of the U.S. east coast. These swells are likely to cause dangerous surf and rip current conditions for the next several days in these areas. FORECAST POSITIONS AND MAX WINDS INIT 17/1500Z 31.0N 71.9W 80 KT 90 MPH 12H 18/0000Z 32.0N 71.8W 80 KT 90 MPH 24H 18/1200Z 33.6N 71.8W 75 KT 85 MPH 36H 19/0000Z 35.2N 71.8W 70 KT 80 MPH 48H 19/1200Z 36.7N 71.8W 70 KT 80 MPH 72H 20/1200Z 39.6N 70.4W 60 KT 70 MPH 96H 21/1200Z 40.0N 67.5W 55 KT 65 MPH 120H 22/1200Z 39.5N 65.5W 50 KT 60 MPH...POST-TROPICAL $$ Forecaster Cangialosi

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