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Hurricane Lorenzo Forecast Discussion Number 30
2019-09-29 22:45:39| National Hurricane Center (Atlantic)
Issued at 500 PM AST Sun Sep 29 2019 000 WTNT43 KNHC 292045 TCDAT3 Hurricane Lorenzo Discussion Number 30 NWS National Hurricane Center Miami FL AL132019 500 PM AST Sun Sep 29 2019 The cloud pattern has continued to degrade throughout the day with cold cloud tops filling in the eye, with a gradual erosion of the convection over the southwest quadrant. A recent AMSR2 pass confirms that the eyewall is indeed open on the western side, and suggests there may be another eyewall replacement cycle occurring. The NOAA Hurricane Hunters are currently performing multiple experimental flights inside and around Lorenzo, and are providing NHC with valuable data. The wind data from the SFMR are indicating that the hurricane-force winds extend outward farther than previously thought, about 60-70 n mi from the center in all quadrants. The aircraft also reported an adjusted minimum central pressure of 948 mb, a peak flight level wind of 99 kt, and an image capture from an on-board radar that confirmed the break in the eyewall. The available objective and subjective intensity estimates range from 102 kt to 114 kt. Based on a compromise of these data, the initial intensity has been set at 100 kt, but this may be a little generous given much lower dropsonde wind speeds measured by the aircraft. Lorenzo continues north-northeastward at 9 kt through a weakness in the subtropical ridge. A mid-latitude trough will approach Lorenzo from the west in a couple of days. Increasing southwesterly flow ahead of the trough will force the hurricane to turn northeastward and accelerate beginning on Monday. The forecast track confidence remains very high through 48 hours, and the new forecast is essentially an update of the previous one. By 72 hours, the guidance continues to diverge significantly, likely due to how they are handling the interaction between Lorenzo and a larger extratropical cyclone to its north late in the forecast period. The ECMWF/UKMET do not have Lorenzo being absorbed into the larger low. Instead, they track Lorenzo to the east-northeast toward Europe ahead of the associated upper trough. The rest of the guidance has Lorenzo absorbed into the low several hundred miles west of the British Isles. The forecast track confidence remains low beyond 72 hours, and was nudged just a little to the left from the previous advisory. The aircraft near-surface dropsonde data suggests that Lorenzo is moving over cooler waters of 24-25 degrees C, a few degrees cooler than model guidance indicates, due to the upwelling of the waters with lower oceanic heat content. The environmental conditions for the next 48 hours are characterized by moderate southwesterly shear, decent moisture, and strong upper-level divergence. Due to the presence of the shear and cooler waters, gradual weakening is anticipated for the next couple of days. By 72 hours, much stronger shear and the interaction with the approaching mid-latitude trough should cause the cyclone to weaken at a faster rate and begin to transition to an extratropical cyclone. By 96 hours or so, extratropical transition is expected to be complete. The official intensity forecast was adjusted lower than the previous one through 48 hours, and then is similar thereafter. This solution is near the various multimodel consensus aids. Key Messages: 1. Lorenzo is a large and powerful hurricane, and its hurricane- and tropical-storm-force wind fields are expected to expand further during the next several days. Regardless of Lorenzo's exact track near the Azores, strong winds are becoming increasingly likely on those islands Tuesday night and Wednesday, and residents there should monitor the progress of the hurricane. Watches could be issued for those islands later today or tonight. 2. Large swells generated by Lorenzo will continue to spread across much of the north Atlantic basin during the next few days. These swells will produce life-threatening surf and rip currents. FORECAST POSITIONS AND MAX WINDS INIT 29/2100Z 26.9N 44.2W 100 KT 115 MPH 12H 30/0600Z 28.2N 43.6W 90 KT 105 MPH 24H 30/1800Z 30.1N 42.6W 85 KT 100 MPH 36H 01/0600Z 32.4N 40.6W 85 KT 100 MPH 48H 01/1800Z 35.6N 37.0W 80 KT 90 MPH 72H 02/1800Z 44.6N 26.3W 70 KT 80 MPH 96H 03/1800Z 52.2N 17.2W 55 KT 65 MPH...POST-TROP/EXTRATROP 120H 04/1800Z 55.0N 15.9W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ Forecaster Latto
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Hurricane Lorenzo Forecast Discussion Number 29
2019-09-29 16:57:04| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Sun Sep 29 2019 000 WTNT43 KNHC 291456 TCDAT3 Hurricane Lorenzo Discussion Number 29 NWS National Hurricane Center Miami FL AL132019 1100 AM AST Sun Sep 29 2019 Satellite and microwave imagery are indicating that Lorenzo is now weakening. A recent microwave pass showed a broken eyewall as well as dry air in the southwestern quadrant. Over the past hour, the eye has begun to fill in. However, outflow remains excellent and cloud tops remain very cold near the center of the hurricane. A blend of the latest CI values from TAFB and SAB as well as a recent subjective intensity estimate from UW-CIMSS suggest the initial intensity is now 125 kt. Lorenzo is moving north-northeastward at 9 kt through a weakness in the subtropical ridge. A mid-latitude trough will approach Lorenzo from the west in a couple of days. Increasing southwesterly flow ahead of the trough will force the hurricane to turn northeastward and accelerate beginning on Monday. The forecast track confidence is very high through 72 hours, and the new forecast is in good agreement with the tightly clustered consensus guidance and the previous forecast. Beyond 72 hours, the guidance now diverges significantly, likely due to how they are handling the interaction between Lorenzo and a larger extratropical cyclone near Greenland late in the forecast period. The majority of the guidance has shifted to the west by several hundred miles over the past couple of runs. However, there remains significant spread between the operational UKMET/ECMWF which take what's left of Lorenzo toward the British Isles, and the solutions that absorb the cyclone into the larger system well over 1000 miles to the west. Based on the recent shift in the models and the large spread, the official forecast was only adjusted a little to the left and lies well to the right of the consensus aids. Needless to say, the forecast track confidence beyond 72 hours is low at the moment, and may need further adjustments in the next couple of advisories. Lorenzo reached its peak intensity last night, and the intensity guidance is in good agreement that the hurricane will steadily weaken over the next several days due to increasing southwesterly shear, dry air entrainment, and progressively cooler SSTs. The NOAA Hurricane Hunters are still scheduled to investigate Lorenzo later today, and the data they collect should provide a better assessment of the hurricane's intensity and structure. In a few days, Lorenzo will interact with a frontal zone and begin transitioning to an extratropical cyclone. This transition is expected to be complete by 96 hours. It is important to note that although Lorenzo is forecast to weaken through the forecast period, the wind field is expected to expand at the same time, with tropical-storm-force and 50 kt winds forecast to extend over 300 n mi/ 160 n mi respectively from the center in 72 hours. The latest intensity forecast is similar to the previous one, and it is near the HFIP corrected consensus HCCA. Earlier input from the Tropical Analysis and Forecast Branch here at NHC indicates that the large wind field of Lorenzo and its expected faster forward motion in a few days will likely lead to extreme enhancement of the wave field and wave growth over the southeastern portion of the circulation. Key Messages: 1. Lorenzo is a large and powerful hurricane, and its hurricane- and tropical-storm-force wind fields are expected to expand further during the next several days. Regardless of Lorenzo's exact track near the Azores, strong winds are becoming increasingly likely on those islands Tuesday night and Wednesday, and residents there should monitor the progress of the hurricane. Watches could be issued for those islands later today or tonight. 2. Large swells generated by Lorenzo will continue to spread across much of the north Atlantic basin during the next few days. These swells will produce life-threatening surf and rip currents. FORECAST POSITIONS AND MAX WINDS INIT 29/1500Z 25.9N 44.4W 125 KT 145 MPH 12H 30/0000Z 27.2N 43.9W 115 KT 130 MPH 24H 30/1200Z 28.9N 43.0W 105 KT 120 MPH 36H 01/0000Z 31.0N 41.6W 100 KT 115 MPH 48H 01/1200Z 33.7N 38.9W 95 KT 110 MPH 72H 02/1200Z 42.0N 29.0W 80 KT 90 MPH 96H 03/1200Z 50.0N 18.4W 65 KT 75 MPH...POST-TROP/EXTRATROP 120H 04/1200Z 54.9N 11.6W 50 KT 60 MPH...POST-TROP/EXTRATROP $$ Forecaster Latto
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Tropical Storm Narda Forecast Discussion Number 5
2019-09-29 16:56:36| National Hurricane Center (East Pacific)
Issued at 1000 AM CDT Sun Sep 29 2019 000 WTPZ41 KNHC 291456 TCDEP1 Tropical Storm Narda Discussion Number 5 NWS National Hurricane Center Miami FL EP162019 1000 AM CDT Sun Sep 29 2019 The center of Narda either re-formed to the northwest or accelerated its forward motion during the night, as surface observations from Mexico and satellite imagery indicate that it is now located along the coast of Mexico near Lazaro Cardenas. The initial intensity is held at 40 kt based on the Mexican observations and little change in the satellite intensity estimates since the last advisory. First-light visible imagery suggests that the cyclone's circulation is elongated east-west, with the center located on the eastern side of the elongation. The initial motion is a rather uncertain 325/13 kt. Over the next couple of days, Narda will be steered generally northwestward along the southwestern periphery of a large high pressure area. After that time, a mid- to upper-level trough approaching the northern Baja California peninsula from the west should cause the system to turn north-northwestward. The new forecast track is parallel to, but moved significantly to the right of, the previous forecast due to the initial position and motion, and it keeps the center over portions of western Mexico for the next 12-24 hours before bringing the system over the southeastern and eastern portions of the Gulf of California. The intensity forecast is highly uncertain. The official forecast will follow the scenario of the previous forecast in calling for Narda to weaken to a depression while over Mexico, and then call for some re-intensification later in the forecast period when the system emerges over water in a light shear environment. However, there are two alternative scenarios. The most likely of these is that the circulation dissipates as it passes over the mountains of western Mexico, which is a distinct possibility if the system goes as far inland as currently forecast. The least likely is that the center reforms offshore, which could lead to significant changes in both the intensity and the track forecasts. The primary threat from Narda is very heavy rainfall, which should result in life-threatening flash flooding and mudslides over portions of the southern coast of Mexico. Rainfall totals of up to 15 inches are possible. FORECAST POSITIONS AND MAX WINDS INIT 29/1500Z 18.1N 102.1W 40 KT 45 MPH 12H 30/0000Z 19.3N 103.6W 30 KT 35 MPH...INLAND 24H 30/1200Z 21.5N 105.6W 25 KT 30 MPH...OVER WATER 36H 01/0000Z 23.2N 107.3W 30 KT 35 MPH 48H 01/1200Z 24.5N 108.6W 35 KT 40 MPH 72H 02/1200Z 26.5N 109.9W 35 KT 40 MPH 96H 03/1200Z 28.0N 110.5W 25 KT 30 MPH...INLAND 120H 04/1200Z...DISSIPATED $$ Forecaster Beven
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Hurricane Lorenzo Forecast Discussion Number 28
2019-09-29 10:33:33| National Hurricane Center (Atlantic)
Issued at 500 AM AST Sun Sep 29 2019 000 WTNT43 KNHC 290833 TCDAT3 Hurricane Lorenzo Discussion Number 28 NWS National Hurricane Center Miami FL AL132019 500 AM AST Sun Sep 29 2019 The satellite appearance of Lorenzo is not quite as impressive as it was several hours ago. Although the eye is still very distinct, the cloud tops are not as cold in the eyewall and there are a few dry slots evident beyond the inner core. The initial wind speed is lowered just slightly to 135 kt, but based on the latest satellite estimates this is probably generous. The NOAA Hurricane Hunters are scheduled to investigate Lorenzo later today, and the data they collect should provide a better assessment of the hurricane's intensity and structure. Very intense hurricanes like Lorenzo are usually not able to maintain their intensity for very long. Since Lorenzo will be moving toward cooler waters and into an environment of drier air and higher wind shear during the next several days, steady weakening is forecast. Lorenzo is now expected to become extratropical by day 4, when the cyclone will be over SSTs colder than 20 C. The NHC intensity forecast is in good agreement with the consensus models, IVCN, IVDR, and HCCA. Lorenzo is still moving northward at 9 kt through a break in the Atlantic subtropical ridge. A mid- to upper-level trough currently over eastern Canada is expected to amplify when it reaches the central Atlantic, which should cause Lorenzo to accelerate to the northeast during the next few days. This motion should take the core of Lorenzo near or just west of the Azores late Tuesday and Wednesday. After that time, there are significant differences in the models on whether or not Lorenzo interacts with an extratropical low over the north Atlantic. The ECMWF and UKMET models show little interaction with that low and show Lorenzo moving east-northeastward in the westerlies toward northwestern France, Ireland, and the United Kingdom. On the other hand, the GFS, HWRF, and HMON models show Lorenzo rotating around the eastern side of the low and remaining over the Atlantic. The spread in the models is incredibly large, about 1300 n mi by day 5. Given the high uncertainty at this time, only small changes were made to the NHC track forecast, and this one favors the UKMET and ECMWF solutions. However, confidence in the long-term track is very low and adjustments may be needed later today. The Tropical Analysis and Forecast Branch here at NHC provided input that the large wind field of Lorenzo and its expected faster forward motion in a few days will likely lead to extreme enhancement of the wave field and wave growth over the southeastern portion of the circulation. Key Messages: 1. Lorenzo is a large and powerful hurricane, and its hurricane- and tropical-storm-force wind fields are expected to expand further during the next several days. Regardless of Lorenzo's exact track near the Azores, strong winds are becoming increasingly likely on those islands Tuesday night and Wednesday, and residents there should monitor the progress of the hurricane. 2. Large swells generated by Lorenzo will continue to spread across much of the north Atlantic basin during the next few days. These swells will produce life-threatening surf and rip currents. FORECAST POSITIONS AND MAX WINDS INIT 29/0900Z 25.1N 44.6W 135 KT 155 MPH 12H 29/1800Z 26.4N 44.2W 125 KT 145 MPH 24H 30/0600Z 28.0N 43.5W 115 KT 130 MPH 36H 30/1800Z 29.9N 42.5W 110 KT 125 MPH 48H 01/0600Z 32.2N 40.5W 105 KT 120 MPH 72H 02/0600Z 39.4N 32.1W 90 KT 105 MPH 96H 03/0600Z 47.8N 20.0W 70 KT 80 MPH...POST-TROP/EXTRATROP 120H 04/0600Z 53.5N 10.0W 55 KT 65 MPH...POST-TROP/EXTRATROP $$ Forecaster Cangialosi
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Tropical Storm Narda Forecast Discussion Number 4
2019-09-29 10:32:28| National Hurricane Center (East Pacific)
Issued at 400 AM CDT Sun Sep 29 2019 000 WTPZ41 KNHC 290832 TCDEP1 Tropical Storm Narda Discussion Number 4 NWS National Hurricane Center Miami FL EP162019 400 AM CDT Sun Sep 29 2019 Satellite images and Acapulco radar data show that the storm has become a little better organized with some evidence of banding features. Upper-level outflow is fairly well defined over the southern semicircle of the circulation while the cyclone continues to experience some northeasterly shear. Based on data from a scatterometer overpass, the current intensity is set at 40 kt which is also the mean of Dvorak estimates from TAFB and SAB. The intensity forecast for Narda is problematic and uncertain, since the future strength of the cyclone depends on how much the cyclone will interact with the mountainous land mass of southwestern Mexico during the next few days. Some of the models, such as the ECMWF and GFS, take the cyclone inland within the next 24 hours and do not show the system recovering from its land interaction in 24-48 hours. A little more strengthening should occur today, assuming the center remains offshore. The official intensity forecast assumes that the center will move along the coast within the next day or so, and this would cause some weakening and disruption of the circulation. The NHC intensity forecast is in fairly close agreement with the LGEM guidance. The center is not easy to locate, but my best estimate of initial motion is northwestward or 315/7 kt. Over the next couple of days, the tropical cyclone is likely to move generally northwestward along the southwestern periphery of a large high pressure area. Later in the period, a trough approaching the northern Baja California peninsula should cause the system to turn toward the north-northwest. The official forecast is similar to the previous one, and close to the corrected dynamical model consensus guidance. The primary threat from Narda is very heavy rainfall, which should result in life-threatening flash flooding and mudslides over portions of the southern coast of Mexico. Rainfall totals of up to 15 inches are possible. FORECAST POSITIONS AND MAX WINDS INIT 29/0900Z 16.0N 101.0W 40 KT 45 MPH 12H 29/1800Z 17.4N 102.4W 45 KT 50 MPH 24H 30/0600Z 19.3N 104.6W 35 KT 40 MPH...INLAND 36H 30/1800Z 21.3N 106.4W 30 KT 35 MPH 48H 01/0600Z 22.8N 107.9W 35 KT 40 MPH 72H 02/0600Z 25.0N 109.5W 35 KT 40 MPH 96H 03/0600Z 26.5N 110.0W 25 KT 30 MPH 120H 04/0600Z 27.5N 110.5W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Pasch
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