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Potential Tropical Cyclone Sixteen-E Forecast Discussion Number 1

2019-09-28 16:51:47| National Hurricane Center (East Pacific)

Issued at 1000 AM CDT Sat Sep 28 2019 000 WTPZ41 KNHC 281451 TCDEP1 Potential Tropical Cyclone Sixteen-E Discussion Number 1 NWS National Hurricane Center Miami FL EP162019 1000 AM CDT Sat Sep 28 2019 The area of disturbed weather along the southwestern coast of Mexico is gradually becoming better organized. There is no evidence of a well-defined center at this time, but satellite animation suggests that a circulation could be forming just south of Acapulco. Since there is a risk of tropical-storm-force winds along the coast of Mexico, the government of Mexico has issued a Tropical Storm Warning for a portion of southwestern coast, and advisories have been initiated on Potential Tropical Cyclone 16-E. Earlier ASCAT data indicate that the disturbance has been producing winds of about 30 kt, mostly within its southern portion. The large envelope of the disturbance is interacting with the high terrain of southern Mexico, and the environment is not ideal for strengthening, but it is good enough for the disturbance to reach tropical storm status. By the end of the forecast period, the shear is expected to be high, and the system should weaken. The initial motion is obviously highly uncertain since there is not a good center to track. The best estimate is toward the northwest or 315 degrees at 11 kt. High pressure over the Gulf of Mexico will continue to steer the disturbance or the cyclone toward the northwest and then north-northwest very close to the southwestern coast of Mexico, and then into the Gulf of California. This is the solution provided by the reliable models. If the system develops its center closer to the coast, there is a chance that the circulation moves inland earlier than anticipated resulting in faster weakening. Regardless of how strong the system becomes, torrential rains are expected along the southwestern coast of Mexico during the next few days. FORECAST POSITIONS AND MAX WINDS INIT 28/1500Z 14.9N 100.4W 30 KT 35 MPH...POTENTIAL TROP CYCLONE 12H 29/0000Z 16.0N 101.5W 35 KT 40 MPH...TROPICAL STORM 24H 29/1200Z 17.5N 103.5W 40 KT 45 MPH 36H 30/0000Z 19.5N 105.5W 40 KT 45 MPH 48H 30/1200Z 22.0N 107.5W 40 KT 45 MPH 72H 01/1200Z 26.0N 111.0W 30 KT 35 MPH 96H 02/1200Z 27.0N 111.5W 25 KT 30 MPH 120H 03/1200Z 29.0N 112.0W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Avila

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Hurricane Lorenzo Forecast Discussion Number 24

2019-09-28 16:47:46| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Sat Sep 28 2019 000 WTNT43 KNHC 281447 TCDAT3 Hurricane Lorenzo Discussion Number 24 NWS National Hurricane Center Miami FL AL132019 1100 AM AST Sat Sep 28 2019 Lorenzo appears to be in the final stages of an eyewall replacement. 37-GHz GCOM imagery from overnight suggested that a smaller inner eyewall was embedded within a larger eye, and the new eyewall now extends 40-45 n mi from the center of circulation. An eye has also reappeared in GOES-16 visible and infrared satellite imagery during the past several hours. Based on Dvorak intensity estimates of T5.5/102 kt from TAFB and SAB, and an ADT estimate of T5.3/97 kt, Lorenzo's intensity is still estimated to be 100 kt. Although the hurricane seems to be wobbling a bit, fixes indicate that it has generally turned northward with an initial motion of 350/9 kt. The track forecast remains straightforward, with very little spread among the models and their ensembles. Lorenzo is expected to be nudged north-northeastward and then northeastward starting in 36 hours by strong ridging building over the western Atlantic. The northeastward motion is expected to increase on day 3 when Lorenzo is picked up by a strong deep-layer trough over the north Atlantic, and that acceleration is forecast to continue through day 5. The NHC track forecast lies near the consensus aids and is very similar to the previous forecast. A little bit of west-southwesterly shear continues over Lorenzo, but it's not strong enough to disrupt the circulation significantly. Only a very slow, gradual weakening is forecast during the next 3 days, matching what is indicated by many of the intensity models. Extratropical transition is expected to have begun by day 4 while Lorenzo is moving near the Azores, but that process is not expected to be complete until day 5. Although Lorenzo's winds are forecast to decrease a bit during the extratropical transition due to stronger shear and cold waters, the cyclone is expected to maintain hurricane-force winds through the end of the forecast period. Lorenzo's wind field will remain large, and the hurricane-force wind radii are expected to grow in size during the next couple of days. In addition, large swells continue to radiate outward away from the hurricane and will reach much of the western and northern side of the Atlantic basin in a few days. FORECAST POSITIONS AND MAX WINDS INIT 28/1500Z 22.5N 44.8W 100 KT 115 MPH 12H 29/0000Z 23.8N 44.6W 100 KT 115 MPH 24H 29/1200Z 25.6N 44.2W 95 KT 110 MPH 36H 30/0000Z 27.1N 43.7W 95 KT 110 MPH 48H 30/1200Z 28.8N 43.0W 90 KT 105 MPH 72H 01/1200Z 33.3N 39.3W 90 KT 105 MPH 96H 02/1200Z 40.5N 29.5W 80 KT 90 MPH 120H 03/1200Z 51.0N 16.5W 70 KT 80 MPH...POST-TROP/EXTRATROP $$ Forecaster Berg

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Hurricane Lorenzo Forecast Discussion Number 23

2019-09-28 10:56:13| National Hurricane Center (Atlantic)

Issued at 500 AM AST Sat Sep 28 2019 000 WTNT43 KNHC 280856 TCDAT3 Hurricane Lorenzo Discussion Number 23 NWS National Hurricane Center Miami FL AL132019 500 AM AST Sat Sep 28 2019 Lorenzo's tilt has grown this morning. AMSR2 imagery at 0505 UTC showed a 20 n mi displacement between the low- and mid-level centers of the hurricane, a consequence of persistent westerly wind shear. Satellite-based intensity estimates vary greatly, from 77 to 110 kt, so the intensity is set to 100 kt as a compromise of all available data. Despite the decrease in Lorenzo's maximum winds during the past 24 hours, earlier ASCAT-C data showed that its hurricane-force wind field has expanded, and now reaches up to 45 n mi to the northeast of the center. The lower initial intensity resulted in a slightly lower intensity forecast through most of the period. The wind shear affecting the cyclone is forecast to continue, and a slow decrease in Lorenzo's peak winds is still expected during the next several days. The official intensity forecast is very near the intensity consensus. Despite the expected decrease in intensity, the hurricane is not forecast to decrease in size, and in fact Lorenzo's hurricane-force wind field could increase further by next week. Because of that, users are urged to not focus on the exact intensity of Lorenzo since the cyclone will likely remain a powerful storm well into next week. By 120 h, all of the global models indicate that Lorenzo will become post-tropical, and so does the NHC forecast. The aforementioned microwave data was very helpful in identifying Lorenzo's center location. The hurricane has continued to move left of the forecast track, and the initial motion estimate is 330/9 kt. Despite Lorenzo's recent tendency to move farther west than anticipated, the hurricane is still forecast to turn northward soon. After continuing northward and north-northeastward for a day or two, Lorenzo should accelerate toward the northeast ahead of a deep mid-latitude trough approaching from the west by mid-week. The NHC track forecast has been shifted slightly left for the first 48 h to account for Lorenzo's recent motion, but it is very similar to the previous forecast at 72 h and beyond. The models are in excellent agreement for the first 3 days of the forecast but the uncertainty grows by the end of the period, primarily due to differences in the forecast forward speed of the cyclone as it recurves and becomes post-tropical. FORECAST POSITIONS AND MAX WINDS INIT 28/0900Z 21.4N 44.8W 100 KT 115 MPH 12H 28/1800Z 22.7N 44.8W 95 KT 110 MPH 24H 29/0600Z 24.5N 44.7W 90 KT 105 MPH 36H 29/1800Z 26.0N 44.2W 90 KT 105 MPH 48H 30/0600Z 27.6N 43.5W 85 KT 100 MPH 72H 01/0600Z 31.5N 40.9W 85 KT 100 MPH 96H 02/0600Z 38.0N 32.5W 80 KT 90 MPH 120H 03/0600Z 48.0N 19.0W 70 KT 80 MPH...POST-TROP/EXTRATROP $$ Forecaster Zelinsky

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Hurricane Lorenzo Forecast Discussion Number 22

2019-09-28 04:36:39| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Fri Sep 27 2019 000 WTNT43 KNHC 280236 TCDAT3 Hurricane Lorenzo Discussion Number 22 NWS National Hurricane Center Miami FL AL132019 1100 PM AST Fri Sep 27 2019 Lorenzo's cloud pattern has continued to deteriorate this evening. A series of SSMI and GMI microwave overpasses revealed inner core erosion, particularly in the south portion. The images also showed a significant south to north vertical tilt of the cyclone, indicative of the moderate southwesterly shear undercutting the impressive upper-tropospheric diffluent flow. A blend of all the available subjective and objective satellite intensity estimates, as well as an earlier SATCON analysis, yields an initial intensity of 105 kt for this advisory. Lorenzo will remain over warm oceanic sea surface temperatures for the next 3 days. Nonetheless, the stiff southwesterly shear should inhibit strengthening, although there is a slight chance of short-term fluctuations in intensity caused by eyewall replacement cycles. Beyond the 72 hour period, Lorenzo is expected to encounter stronger mid-latitude westerlies, move over cooler waters, and undergo extratropical transition as it interacts with a baroclinic zone moving over the central north Atlantic. The NHC forecast is an update of the previous advisory and is based on a blend of the HFIP Corrected Consensus and Florida State Superensemble intensity models. The aforementioned microwave images also indicate that Lorenzo has been moving a little to the left of track, and the initial motion is estimated to be north-northwestward, or 335/8 kt. The song remains the same, no change in the track forecast philosophy. Lorenzo should turn northward and then northeastward during the next few days as it moves around the western periphery of a mid-tropospheric ridge anchored over the eastern Atlantic. Around mid-period, Lorenzo is forecast to accelerate toward the northeast, in the mid-latitude westerly flow, in response to a deep-layer major shortwave trough approaching from the north-central Atlantic. The track forecast has been adjusted slightly to the left of the previous one and is close to the various consensus aids. The wind radii have been adjusted using 2308 UTC METOP-B scatterometer data. The forecast wind radii, beyond the 48 hour period, is based primarily on the RVCN global consensus. FORECAST POSITIONS AND MAX WINDS INIT 28/0300Z 20.8N 44.1W 105 KT 120 MPH 12H 28/1200Z 21.9N 44.5W 105 KT 120 MPH 24H 29/0000Z 23.7N 44.5W 100 KT 115 MPH 36H 29/1200Z 25.4N 44.1W 100 KT 115 MPH 48H 30/0000Z 27.0N 43.4W 95 KT 110 MPH 72H 01/0000Z 30.7N 41.3W 95 KT 110 MPH 96H 02/0000Z 36.5N 34.6W 90 KT 105 MPH 120H 03/0000Z 45.5N 22.9W 75 KT 85 MPH...POST-TROP/EXTRATROP $$ Forecaster Roberts

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Hurricane Lorenzo Forecast Discussion Number 21

2019-09-27 22:36:05| National Hurricane Center (Atlantic)

Issued at 500 PM AST Fri Sep 27 2019 000 WTNT43 KNHC 272035 TCDAT3 Hurricane Lorenzo Discussion Number 21 NWS National Hurricane Center Miami FL AL132019 500 PM AST Fri Sep 27 2019 The satellite appearance of Lorenzo has degraded further since the last advisory, with only a hint of an eye still apparent in visible imagery and the cold cloud tops in the eyewall becoming very asymmetric in infrared imagery. A recent SSMI/S overpass shows that the southern portion of the eyewall has eroded, possibly due to shear or dry air intrusion. The microwave imagery also suggests an outer convective band is forming, but it is not yet well enough defined to call it an outer eyewall. Satellite intensity estimates have continued to decrease, and the initial intensity is lowered to 110 kt as a blend of the various estimates. The hurricane continues to have excellent outflow in the northern semicircle. The initial motion remains 330/12 kt. There is no change in the track forecast philosophy or the forecast confidence, as Lorenzo should turn northward and then northeastward during the next few days as it moves around the western edge of a mid-level ridge centered over the eastern Atlantic. Later in the forecast period, the cyclone is expected to accelerate northeastward in the mid-latitude westerlies ahead of a deep-layer trough approaching from the west. The track guidance for this advisory, while it remains tightly clustered in direction, is a little slower than the previous guidance. Based on this, the new forecast track is just a little slower than the previous forecast. Lorenzo will be passing over sea surface temperatures of 27-28C for the next 48-72 h. However, it will be in an environment of moderate vertical shear due to an upper-level trough not far to the west. The intensity guidance responds to this by showing gradual weakening during this time, and the new intensity forecast follows the trend of the guidance. There is a possibility of fluctuations in intensity caused by eyewall replacement cycles superimposed on this weakening trend. After 72 h, the hurricane should encounter stronger mid-latitude westerlies, move over cooler sea surface temperatures, and eventually merge with the above-mentioned deep-layer trough. As this occurs, Lorenzo is forecast to undergo extratropical transition, with this being complete by 120 h. Current indications from the global models are that Lorenzo will retain hurricane strength through the transition. FORECAST POSITIONS AND MAX WINDS INIT 27/2100Z 20.3N 43.6W 110 KT 125 MPH 12H 28/0600Z 21.6N 44.1W 105 KT 120 MPH 24H 28/1800Z 23.3N 44.3W 100 KT 115 MPH 36H 29/0600Z 25.0N 44.0W 100 KT 115 MPH 48H 29/1800Z 26.6N 43.3W 100 KT 115 MPH 72H 30/1800Z 30.3N 41.1W 95 KT 110 MPH 96H 01/1800Z 35.5N 36.0W 90 KT 105 MPH 120H 02/1800Z 44.0N 26.5W 80 KT 90 MPH...POST-TROP/EXTRATROP $$ Forecaster Beven

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