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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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