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Tropical Depression Olaf Forecast Discussion Number 14
2021-09-11 04:49:15| National Hurricane Center (East Pacific)
Issued at 900 PM MDT Fri Sep 10 2021 000 WTPZ45 KNHC 110249 TCDEP5 Tropical Depression Olaf Discussion Number 14 NWS National Hurricane Center Miami FL EP152021 900 PM MDT Fri Sep 10 2021 Olaf continues to rapidly weaken this evening as the low-level circulation spins down while devoid of any deep convection. Olaf has now failed to produce deep convection for more than 12 hours, and barring any diurnal convective bursts tonight, could become a remnant low as soon as tomorrow morning. Winds along the coast of Baja California Sur are gradually subsiding, and the most recent TAFB and SAB subjective Dvorak data-T intensity estimates support downgrading Olaf to a tropical depression this advisory, with maximum sustained winds of 30 kt. The tropical depression's track continues to bend leftward as it pulls away from Baja California Sur, with the latest motion estimate now due west at 270/7 kt. Now that Olaf has become a shallow cyclone, it will primarily be steered by the low-level flow around a extensive subtropical ridge located to the northwest. This flow will continue to turn Olaf to the left with a southwestward motion beginning in the next 24 hours, which should continue until the cyclone dissipates. The official NHC track forecast was nudged a little to the south and east, following the multi-model consensus aids. A combination of cooling sea-surface temperatures (below 26 C) and very dry-mid level air (below 40 percent relative humidity) should ensure that Olaf will soon meet a swift end as a tropical cyclone. The official NHC intensity forecast now makes Olaf a remnant low in 12 hours, and spins the circulation down to 20 kt until eventual dissipation over the open east Pacific. FORECAST POSITIONS AND MAX WINDS INIT 11/0300Z 24.7N 113.3W 30 KT 35 MPH 12H 11/1200Z 24.7N 114.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 24H 12/0000Z 24.4N 115.3W 20 KT 25 MPH...POST-TROP/REMNT LOW 36H 12/1200Z 23.6N 116.3W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 13/0000Z 22.7N 117.6W 20 KT 25 MPH...POST-TROP/REMNT LOW 60H 13/1200Z 21.7N 118.9W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 14/0000Z 21.0N 120.1W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 15/0000Z 20.6N 121.3W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 16/0000Z...DISSIPATED $$ Forecaster Papin
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Hurricane Larry Forecast Discussion Number 42
2021-09-11 04:48:46| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Fri Sep 10 2021 000 WTNT42 KNHC 110248 TCDAT2 Hurricane Larry Discussion Number 42 NWS National Hurricane Center Miami FL AL122021 1100 PM AST Fri Sep 10 2021 Satellite imagery and data from Canadian radars indicate that Larry is maintaining good central convective banding in the northeastern semicircle, and based on this it is still a tropical cyclone at this time. The maximum intensity is held at 70 kt based mainly on recently-received scattterometer data showing 64-67 kt winds to the east and southeast of the center. Surface observations indicate that tropical storm conditions are spreading into southeastern Newfoundland, and hurricane condition should move onshore during the next few hours as the center makes landfall. After landfall, Larry is expected to quickly lose its tropical cyclone characteristics and become a strong extratropical low over the Labrador Sea. The cyclone is forecast to dissipate after 24 h as it merges with a developing mid-latitude low currently to its northwest. Larry is moving rapidly toward the north-northeast with an initial motion of 030/41. This general motion should continue until Larry merges with the other low pressure area. The new official forecast track is little changed from the previous track and is in the middle of the tightly clustered guidance models. Key Messages: 1. Larry will move over portions of southeastern Newfoundland during the next several hours as it undergoes transition to a hurricane-force post-tropical cyclone. Hurricane conditions, a dangerous storm surge, and heavy rainfall are expected in portions of southeastern Newfoundland where a Hurricane Warning in effect. 2. Large swells generated by Larry will continue to affect the Bahamas, Bermuda, and the east coast of the United States and Atlantic Canada through Saturday night. These swells will cause life-threatening surf and rip current conditions, and beachgoers and other interests along these coasts are urged to follow the guidance of lifeguards and local officials. FORECAST POSITIONS AND MAX WINDS INIT 11/0300Z 46.8N 54.9W 70 KT 80 MPH 12H 11/1200Z 51.9N 49.5W 65 KT 75 MPH...POST-TROP/EXTRATROP 24H 12/0000Z 56.8N 44.7W 60 KT 70 MPH...POST-TROP/EXTRATROP 36H 12/1200Z...DISSIPATED $$ Forecaster Beven
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Tropical Storm Olaf Forecast Discussion Number 13
2021-09-10 22:45:35| National Hurricane Center (East Pacific)
Issued at 300 PM MDT Fri Sep 10 2021 000 WTPZ45 KNHC 102045 TCDEP5 Tropical Storm Olaf Discussion Number 13 NWS National Hurricane Center Miami FL EP152021 300 PM MDT Fri Sep 10 2021 The low-level center of Olaf is completely exposed in visible satellite imagery this afternoon. The system has been devoid of organized convection since around 1200 UTC, and Olaf is at risk of losing its status as a tropical cyclone overnight if it is unable to generate new convection within the next 12 h. Despite its lack of convection, a weather station at Puerto Cortes measured sustained tropical-storm-force winds several hours ago as the center of Olaf passed very near the observation site, and it has more recently reported several tropical-storm-force gusts. The initial intensity is lowered to 40 kt for this advisory based on the aforementioned surface observations and T2.5/35 kt Dvorak classifications from TAFB and SAB. Olaf has rapidly weakened today, and this weakening trend is expected to continue during the next couple of days. The cyclone will be moving over sub-26 deg C sea-surface temperatures and into a drier, more stable environment that should largely suppress new convective development. Model simulated satellite imagery from the GFS and ECMWF indicate that Olaf will struggle to produce any new convection by tomorrow, and the intensity guidance consensus favors continued weakening as the vortex spins down. The official NHC intensity forecast shows Olaf becoming a 25-kt remnant low by 24 h. The remnant low is forecast to linger around for several days after, but remain weak as it moves over the open waters of the eastern Pacific. The tropical storm has begun moving more westward away from Baja California Sur, and its initial motion is estimated to be west-northwest (295 degrees) at 9 kt. A mid-level ridge building to the north of Olaf should steer the cyclone westward tonight into Saturday. By late Saturday, the shallow cyclone will begin moving southwestward as it is steered around a low-level ridge to its northwest. The official NHC track forecast lies near the middle of the guidance envelope, closest to the multi-model consensus aids. Key Messages: 1. Olaf is moving away from the Baja California peninsula, and lingering tropical storm conditions along portions of the southwestern coast of Baja California Sur are forecast to diminish this evening. 2. Heavy rains associated with Olaf are expected across portions of southern Baja California Sur through tonight. This rainfall may trigger life-threatening flash flooding and mudslides. FORECAST POSITIONS AND MAX WINDS INIT 10/2100Z 24.6N 112.7W 40 KT 45 MPH 12H 11/0600Z 24.8N 113.6W 35 KT 40 MPH 24H 11/1800Z 24.7N 114.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 12/0600Z 24.2N 115.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 12/1800Z 23.3N 117.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 60H 13/0600Z 22.3N 118.3W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 13/1800Z 21.4N 119.7W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 14/1800Z 20.8N 121.7W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 15/1800Z 20.5N 123.0W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Reinhart
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Hurricane Larry Forecast Discussion Number 41
2021-09-10 22:44:09| National Hurricane Center (Atlantic)
Issued at 500 PM AST Fri Sep 10 2021 691 WTNT42 KNHC 102044 TCDAT2 Hurricane Larry Discussion Number 41 NWS National Hurricane Center Miami FL AL122021 500 PM AST Fri Sep 10 2021 Even though Larry is crossing the north wall of the Gulf Stream Current, the hurricane remains well organized and has changed little during the past several hours. Satellite images and radar data indicate that Larry still has an inner core, though the southern side has eroded some. Large curved bands surround the inner core region, with dry slots noted between the core and bands. The initial intensity is held at 70 kt based mostly on the ASCAT data from earlier today, which showed peak winds of around 65 kt to the east of the center. It should be noted that this intensity value is above the Dvorak estimates, which are often not as reliable for high latitude storms like Larry. The earlier ASCAT data confirmed that Larry is a large cyclone with hurricane-force and tropical-storm-force winds extending outward up to 90 n mi and 220 n mi from the center, respectively. Larry is rapidly approaching southeastern Newfoundland, and weather conditions are expected to begin to deteriorate there in a few hours. The hurricane continues to accelerate to the north-northeast, and the latest initial motion estimate is 020/30 kt. An even faster north-northeast to northeast motion is expected during the next day or so as the hurricane moves in the fast flow between a mid- to upper-level trough over the northeastern U.S./eastern Canada and a mid-level ridge over the central Atlantic. This motion should take Larry across southeastern Newfoundland tonight. Larry is then expected to merge with a large extratropical low over the Labrador Sea on Sunday. The NHC track forecast is largely an update of the previous one and near the middle of the tightly clustered models. Larry is expected to maintain its intensity through landfall in Newfoundland tonight. However, a combination of land interaction, much cooler SSTs, and an increase in shear are expected to promote weakening shortly after landfall. Larry should be fully extratropical early Saturday morning when it is forecast to be exiting Newfoundland and moving over the cold waters of the Labrador Sea. The NHC intensity forecast remains close to the GFS model, which often performs well for hurricanes that transition to extratropical cyclones. Key Messages: 1. Larry is forecast to move over portions of southeastern Newfoundland tonight as it undergoes transition to a hurricane-force post-tropical cyclone. Hurricane conditions, a dangerous storm surge, and heavy rainfall are expected in portions of southeastern Newfoundland where a Hurricane Warning in effect. 2. Large swells generated by Larry will continue to affect the Bahamas, Bermuda, and the east coast of the United States and Atlantic Canada through Saturday night. These swells will cause life-threatening surf and rip current conditions, and beachgoers and other interests along these coasts are urged to follow the guidance of lifeguards and local officials. FORECAST POSITIONS AND MAX WINDS INIT 10/2100Z 43.5N 58.2W 70 KT 80 MPH 12H 11/0600Z 48.6N 53.3W 65 KT 75 MPH...POST-TROP/EXTRATROP 24H 11/1800Z 54.9N 46.9W 60 KT 70 MPH...POST-TROP/EXTRATROP 36H 12/0600Z 58.6N 42.4W 60 KT 70 MPH...POST-TROP/EXTRATROP 48H 12/1800Z...DISSIPATED $$ Forecaster Cangialosi
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Tropical Storm Olaf Forecast Discussion Number 12
2021-09-10 16:51:00| National Hurricane Center (East Pacific)
Issued at 900 AM MDT Fri Sep 10 2021 000 WTPZ45 KNHC 101450 TCDEP5 Tropical Storm Olaf Discussion Number 12 NWS National Hurricane Center Miami FL EP152021 900 AM MDT Fri Sep 10 2021 The satellite presentation of Olaf has significantly degraded over the past several hours after the center moved across the southern portion of Baja California Sur overnight. The system's organized convection has collapsed, and infrared satellite imagery indicates cloud top temperatures are rapidly warming near the estimated center position. The initial intensity is lowered to 60 kt for this advisory, which now makes Olaf a tropical storm. This estimate may still be generous, but limited surface observations and radar data make it difficult to confidently assess the intensity. Hopefully, scatterometer data this afternoon will provide more insight into changes in Olaf's surface wind field. The tropical storm has slowed down a bit since last night, and its estimated motion is northwest (310 degrees) at 9 kt. Recent microwave imagery suggests the center of Olaf is just offshore the southwestern coast of Baja California Sur, and the cyclone is likely to move roughly parallel to the coast today. Then, a strong mid-level high pressure ridge centered over the southern Rockies is expected to build westward to the north of Olaf. This ridge should turn Olaf toward the west by tonight, and then toward the southwest through early next week. The official NHC track forecast has been adjusted to the south of the previous forecast once again, in agreement with the latest multi-model consensus aids. Olaf is likely to continue rapidly weakening during the next couple of days. In the short-term, its proximity to the mountainous terrain of the Baja California peninsula will disrupt its ability to sustain organized convection. As Olaf moves away from land, the cyclone will encounter decreasing sea-surface temperatures and very dry mid-level air, which should expedite its transition into a post-tropical cyclone. In fact, the latest GFS and ECMWF model simulated satellite imagery show Olaf becoming completely devoid of convection within the next 24-36 h. The latest NHC intensity forecast shows more rapid weakening than the previous one, primarily based on recent satellite trends and the lower initial intensity. The official forecast remains below the HCCA and IVCN consensus aids, which are inflated by the SHIPS and LGEM models that fail to weaken Olaf during the next 24 h. Key Messages: 1. Olaf is forecast to move along the southwestern coast of the Baja California peninsula today, with tropical storm conditions continuing over southern portions of Baja California Sur through this evening. These winds should diminish tonight as Olaf continues weakening and turns westward away from land. 2. Heavy rains associated with Olaf are expected across portions of southern Baja California Sur through today. This will pose a threat of significant and life-threatening flash flooding and mudslides. FORECAST POSITIONS AND MAX WINDS INIT 10/1500Z 24.1N 111.3W 60 KT 70 MPH 12H 11/0000Z 24.5N 112.4W 50 KT 60 MPH 24H 11/1200Z 24.6N 113.6W 40 KT 45 MPH 36H 12/0000Z 24.3N 114.7W 35 KT 40 MPH...POST-TROPICAL 48H 12/1200Z 23.4N 115.9W 30 KT 35 MPH...POST-TROP/REMNT LOW 60H 13/0000Z 22.4N 117.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 13/1200Z 21.6N 118.6W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 14/1200Z 20.7N 121.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 15/1200Z 20.0N 123.0W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Reinhart
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