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Hurricane Larry Forecast Discussion Number 29

2021-09-07 22:54:19| National Hurricane Center (Atlantic)

Issued at 500 PM AST Tue Sep 07 2021 000 WTNT42 KNHC 072054 TCDAT2 Hurricane Larry Discussion Number 29 NWS National Hurricane Center Miami FL AL122021 500 PM AST Tue Sep 07 2021 After becoming rather ragged-looking in earlier satellite images, Larry's eye has become a little better defined recently, and the surrounding deep convection is more or less maintaining its strength. Observations from a NOAA Hurricane Hunter aircraft show that the central pressure has fallen slightly, to 965 mb. Peak flight-level winds from the aircraft were 110 kt so the advisory intensity is kept at 100 kt. This is also consistent with a Dvorak Current Intensity number from TAFB. Larry continues its northwestward motion at about 320/8 kt. The hurricane should move around the western side of a deep-layer subtropical anticyclone during the next 48-60 hours. After passing Bermuda, the system is likely to accelerate northeastward while moving into the mid-latitude westerlies ahead of a trough moving from the northeastern United States to Atlantic Canada, and move into the far north Atlantic by day 5. The official track forecast stays close to the previous NHC prediction, and remains in good agreement the various model consensus solutions. The hurricane continues to exhibit well-defined upper-level outflow, indicative of weak vertical shear. Over the next couple of days, Larry will be traversing waters of gradually decreasing oceanic heat content. This, combined with some dry mid-level air in the environment, should lead to a gradual decrease in intensity through 48-60 hours. Later in the forecast period, colder waters and strong shear should cause more rapid weakening. By day 4, the global models show Larry merging with a frontal zone. Therefore, the NHC forecast calls for extratropical transition by that time. The official intensity forecast is generally below the statistical-dynamical guidance and above the coupled dynamical hurricane models through 72 hours, but in good agreement with the model consensus aids. Key Messages: 1. Large swells generated by Larry will continue to affect the Lesser Antilles, portions of the Greater Antilles, and the Bahamas through midweek. Significant swells should reach the east coast of the United States and Atlantic Canada by midweek and continue affecting these shores through the end of the week. These swells will likely 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 this week. 2. The center of Larry is forecast to pass east of Bermuda on Thursday, but given Larry's large size, tropical storm conditions are possible there Thursday, along with a risk of heavy rainfall and coastal flooding. A Tropical Storm Watch is in effect for Bermuda and interests there should closely monitor the latest forecast updates. 3. Larry is forecast to move near or over portions of southeastern Newfoundland late Friday and Friday night as it transitions to a hurricane-force post-tropical cyclone. There is a risk of impacts from high winds, rainfall, and storm surge in portions of Newfoundland, and interests there should monitor the progress of Larry and updates to the forecast. FORECAST POSITIONS AND MAX WINDS INIT 07/2100Z 25.1N 56.3W 100 KT 115 MPH 12H 08/0600Z 26.5N 57.4W 95 KT 110 MPH 24H 08/1800Z 28.3N 58.8W 95 KT 110 MPH 36H 09/0600Z 30.5N 60.5W 90 KT 105 MPH 48H 09/1800Z 33.3N 61.7W 90 KT 105 MPH 60H 10/0600Z 36.8N 61.2W 85 KT 100 MPH 72H 10/1800Z 41.7N 58.2W 80 KT 90 MPH 96H 11/1800Z 53.0N 48.0W 65 KT 75 MPH...POST-TROP/EXTRATROP 120H 12/1800Z 60.0N 38.0W 50 KT 60 MPH...POST-TROP/EXTRATROP $$ Forecaster Pasch

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Tropical Depression Fifteen-E Forecast Discussion Number 1

2021-09-07 22:41:22| National Hurricane Center (East Pacific)

Issued at 300 PM MDT Tue Sep 07 2021 000 WTPZ45 KNHC 072041 TCDEP5 Tropical Depression Fifteen-E Discussion Number 1 NWS National Hurricane Center Miami FL EP152021 300 PM MDT Tue Sep 07 2021 Over the past day or so, convection has gradually become better organized in association with the area of low pressure offshore of the coast of southwestern Mexico. There is now a large curved band to the east of the center, and outflow is increasing in all quadrants. Based on the improving convective organization, advisories are being initiated on Tropical Depression Fifteen-E. An ASCAT-B overpass a few hours ago indicated the peak winds associated with the depression were 26 kt, and assuming some undersampling, the initial advisory intensity is set at 30 kt. The depression has been moving slowly west-northwestward today, to the south of a weak mid-level ridge over northwestern Mexico. Another ridge is forecast to begin building from the southwestern United States to over northern Mexico tonight, which should turn the cyclone to the northwest. The system should then gradually accelerate through midweek as it gets caught in the flow between this ridge, and a mid- to upper-level trough to its west. By late in the forecast period, a turn to the west is expected as the cyclone weakens and becomes steered by the low-level flow. The model guidance is generally in good agreement on this scenario, and the NHC track forecast is close to the various model consensus solutions. It should be noted that based on this track forecast, the center of the cyclone would approach within 120 n mi of the southern tip of the Baja California peninsula on Thursday. Therefore, any deviation in the track to the right would increase the chance for impacts to that area. There are very favorable environmental conditions around the depression that should allow for strengthening over the next couple of days. The only inhibiting factor for quick strengthening in the short term appears to be the lack of a tight circulation and inner-core convection. Because of this, the NHC intensity forecast is on the lower end of the guidance through the first 24 hours, nearest to the LGEM, as it appears the HWRF/HMON are a bit too aggressive in intensifying the cyclone during that time. By 24 hours, it is assumed that the inner-core will become better established, and faster strengthening is indicated from 24 to 48 hours. By 72 hours, the system is forecast to begin moving over much cooler waters and into a dry, stable atmospheric environment, which should cause weakening. By this weekend, the cyclone is expected to degenerate into a remnant low. The NHC intensity forecast beyond 24 hours is very near the IVCN consensus. FORECAST POSITIONS AND MAX WINDS INIT 07/2100Z 18.2N 107.9W 30 KT 35 MPH 12H 08/0600Z 18.4N 108.1W 35 KT 40 MPH 24H 08/1800Z 19.0N 108.6W 45 KT 50 MPH 36H 09/0600Z 20.0N 109.3W 55 KT 65 MPH 48H 09/1800Z 21.1N 110.5W 65 KT 75 MPH 60H 10/0600Z 22.4N 112.0W 65 KT 75 MPH 72H 10/1800Z 23.4N 113.7W 55 KT 65 MPH 96H 11/1800Z 24.5N 116.5W 40 KT 45 MPH 120H 12/1800Z 24.5N 118.9W 30 KT 35 MPH...POST-TROP/REMNT LOW $$ Forecaster Latto

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Hurricane Larry Forecast Discussion Number 28

2021-09-07 16:59:38| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Tue Sep 07 2021 000 WTNT42 KNHC 071459 TCDAT2 Hurricane Larry Discussion Number 28 NWS National Hurricane Center Miami FL AL122021 1100 AM AST Tue Sep 07 2021 An Air Force Reserve Unit Hurricane Hunter aircraft investigated Larry a little while ago and found that the hurricane has weakened somewhat. The central pressure has risen to 967 mb, and the eyewall is becoming less well defined. Satellite imagery shows that the eye is still evident but the deep convection has has decreased in coverage and intensity. Using a blend of flight-level and SFMR-observed surface winds from the aircraft gives a current intensity estimate of 100 kt, although this may be generous. The hurricane continues to move northwestward, or 315/8 kt. Larry is forecast to move around the western periphery of a subtropical anticyclone during the next couple of days. By 72 hours, the system should begin to accelerate northeastward on the eastern side of a mid-tropospheric trough moving through the northeastern United States. Thereafter, Larry should be well-embedded in the higher-latitude southwesterly flow, pass near Newfoundland and move into the far North Atlantic as an extratropical cyclone. The official track forecast is essentially the same as the previous one and in very close agreement with the latest NOAA corrected consensus and Florida State University (FSU) Superensemble tracks. Larry is in a low-shear environment with fairly well-defined upper-level outflow. However dry mid-level air and possible upwelling of cooler waters beneath the slow-moving circulation appear to be at least partially responsible for weakening. Since the environment does not appear to be very hostile for the next couple of days, only slow weakening is anticipated. The official intensity forecast for the next 48-72 hours lies below the statistical dynamical Decay-SHIPS guidance and above the coupled- HWRF dynamical model prediction. By 96 hours, the FSU cyclone phase analysis indicates that Larry will have undergone an extratropical transition, and this is also shown in the official forecast. Larry is expected to pass east of Bermuda on Thursday as a large hurricane. Given the expansive size of Larry's wind field and forecast uncertainties, a Tropical Storm Watch has been issued for the island. Key Messages: 1. Large swells generated by Larry will continue to affect the Lesser Antilles, portions of the Greater Antilles, and the Bahamas through midweek. Significant swells should reach the east coast of the United States and Atlantic Canada by midweek and continue affecting these shores through the end of the week. These swells will likely 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 this week. 2. The center of Larry is forecast to pass east of Bermuda on Thursday, but given Larry's large size, tropical storm conditions are possible there Thursday, along with a risk of heavy rainfall and coastal flooding. A Tropical Storm Watch is in effect for Bermuda and interests there should closely monitor the latest forecast updates. FORECAST POSITIONS AND MAX WINDS INIT 07/1500Z 24.4N 55.6W 100 KT 115 MPH 12H 08/0000Z 25.6N 56.6W 95 KT 110 MPH 24H 08/1200Z 27.3N 58.1W 90 KT 105 MPH 36H 09/0000Z 29.3N 59.9W 90 KT 105 MPH 48H 09/1200Z 31.8N 61.3W 90 KT 105 MPH 60H 10/0000Z 34.9N 61.8W 85 KT 100 MPH 72H 10/1200Z 39.0N 60.0W 80 KT 90 MPH 96H 11/1200Z 50.0N 50.0W 65 KT 75 MPH...POST-TROP/EXTRATROP 120H 12/1200Z 58.0N 42.0W 50 KT 60 MPH...POST-TROP/EXTRATROP $$ Forecaster Pasch

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Hurricane Larry Forecast Discussion Number 27

2021-09-07 10:48:57| National Hurricane Center (Atlantic)

Issued at 500 AM AST Tue Sep 07 2021 000 WTNT42 KNHC 070848 TCDAT2 Hurricane Larry Discussion Number 27 NWS National Hurricane Center Miami FL AL122021 500 AM AST Tue Sep 07 2021 Larry has maintained a very warm, pronounced eye with a diameter of around 45 to 50 n mi overnight. However, recent infrared satellite imagery and earlier microwave data show some weaknesses in the western eyewall of the hurricane, potentially signaling the entrainment of some drier air into its inner core. This could be the result of some moderate westerly shear impinging on the system. The initial intensity is lowered to 105 kt for this advisory, based on a 0520 UTC SATCON estimate of 103 kt and T5.5/102 kt current intensity Dvorak estimates from TAFB and SAB. An Air Force Reserve hurricane hunter reconnaissance flight is scheduled to investigate Larry later this morning, which should provide more insight into the hurricane's structure and intensity. Larry is moving toward the northwest at 315/9 kt, as the hurricane is being steered around a subtropical ridge over the central Atlantic. This general motion is expected to continue for the next 48 h or so. By Thursday, the hurricane is forecast to turn northward within the flow between the ridge and an approaching deep-layer trough that will be crossing the northeastern United States. As the trough moves over the western Atlantic, Larry should accelerate northeastward deeper into the mid-latitudes on Friday and Saturday, passing near or over portions of Atlantic Canada. The latest NHC track forecast lies near the HCCA and TVCA consensus aids, and no significant adjustments were made from the previous forecast. Larry is expected to pass east of Bermuda on Thursday as a large hurricane. Given the expansive size of its wind field, a Tropical Storm Watch could be required for the island later today. Although the warm sea-surface temperatures and diminishing vertical wind shear along Larry's forecast track appear favorable during the next couple of days, it may not be able to take advantage of these conditions due to its large size, as well as the potential for another eyewall replacement cycle. As previously noted, Larry's broad wind field and moderate forward speed could also result in some upwelling of cooler waters near its inner core. There remains a split in the intensity guidance, with the statistical-dynamical guidance notably higher than the coupled atmosphere-ocean models. The official NHC intensity forecast shows a gradual weakening of Larry during the next several days. Nonetheless, Larry will remain a forceful hurricane that continues to produce significant swell with far-reaching impacts through the week. After 72 h, Larry should begin its extratropical transition, and the official forecast shows Larry becoming a hurricane-force extratropical cyclone by 96 h. Key Messages: 1. Large swells generated by Larry will continue to affect the Lesser Antilles, portions of the Greater Antilles, and the Bahamas through midweek. Significant swells should reach the east coast of the United States and Atlantic Canada by midweek and continue affecting these shores through the end of the week. These swells will likely 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 this week. 2. Larry is forecast to approach Bermuda during the next couple of days as a large and powerful hurricane, bringing a risk of strong winds, heavy rainfall, and coastal flooding to the island by Thursday. Tropical storm watches could be needed for the island later today, and interests in Bermuda should closely monitor the latest forecast updates. FORECAST POSITIONS AND MAX WINDS INIT 07/0900Z 23.8N 55.1W 105 KT 120 MPH 12H 07/1800Z 24.9N 56.0W 100 KT 115 MPH 24H 08/0600Z 26.5N 57.4W 95 KT 110 MPH 36H 08/1800Z 28.4N 59.1W 95 KT 110 MPH 48H 09/0600Z 30.6N 60.8W 95 KT 110 MPH 60H 09/1800Z 33.3N 61.8W 90 KT 105 MPH 72H 10/0600Z 37.1N 61.0W 85 KT 100 MPH 96H 11/0600Z 47.7N 52.4W 75 KT 85 MPH...POST-TROP/EXTRATROP 120H 12/0600Z 57.0N 43.0W 55 KT 65 MPH...POST-TROP/EXTRATROP $$ Forecaster Reinhart

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Hurricane Larry Forecast Discussion Number 26

2021-09-07 04:53:46| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Mon Sep 06 2021 409 WTNT42 KNHC 070253 TCDAT2 Hurricane Larry Discussion Number 26 NWS National Hurricane Center Miami FL AL122021 1100 PM AST Mon Sep 06 2021 Larry has changed little in geostationary satellite imagery since the NOAA P-3 aircraft left the storm after 2130 UTC. Data from the mission showed that the hurricane possessed a very large wind field, and there were occasional hints in the flight-level wind data of an outer wind maxima trying to develop. The most recent passive microwave imagery from a 2148 UTC SSMIS pass showed some evidence of secondary bands forming away from the primary eyewall, though the inner eye remains large and distinct. Whether or not this will be the start of another eyewall replacement cycle (ERC) remains to be seen. For now, both the subjective Dvorak estimates from SAB and TAFB remain unchanged from earlier today, so Larry's intensity has been maintained at 110 kt for this advisory. The hurricane continues to move to the northwest at 325/9 kt, guided along the southwestern periphery of a prominent subtropical ridge. Larry will reach the westward extent of this ridge in 60-72 hours as a large deep-layer trough approaches from the northeastern United States. The latest guidance now shows this trough capturing Larry towards the end of the forecast period, resulting in an abrupt acceleration to the northeast as the hurricane is steered by the strong westerly flow ahead of the mid-latitude trough. The track guidance continues to be in great agreement with Larry's forecast track, and only a few minor adjustments were needed to the most recent forecast, staying near the middle of the track guidance envelope. This latest forecast continues to show Larry passing to the east of Bermuda on Thursday. However, given Larry's large size, some impacts could still be felt even if the center passes well east, and a tropical storm watch could be needed for the island as soon as tomorrow morning. The intensity forecast for Larry over the next few days is likely to be controlled by changes to its inner-core structure. If another ERC begins soon, this could result in a short-term drop off in maximum sustained winds as the hurricane's wind field expands. As mentioned last night, the broadening wind field, in combination with Larry's slow motion currently at 9 kt, could also result in more ocean upwelling closer to Larry's inner core. While the latest SHIPS guidance depicts warm sea-surface temperatures along the track of Larry over the next 2-3 days, the oceanic heat content in this part of the Atlantic basin is not very high. This might explain why the atmosphere-ocean coupled models (COAMPS-TC, HWRF, HAFS-B) show more significant weakening with a gradually decaying inner-core over cooler upwelled waters. The latest NHC intensity forecast is lower than the previous one, giving a bit more weight to the dynamically coupled hurricane models versus the statistical-dynamical guidance. However, even this latest forecast is higher than the reliable HFIP Corrected Consensus Approach (HCCA). Regardless of these intensity details, Larry is expected to remain a large and powerful hurricane over the next few days. Key Messages: 1. Large swells generated by Larry are affecting the Lesser Antilles and will spread to portions of the Greater Antilles, the Bahamas, and Bermuda tonight and tomorrow. Significant swells should reach the east coast of the United States and Atlantic Canada by midweek and continue affecting these shores through the end of the week. These swells will likely 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 this week. 2. Larry is forecast to approach Bermuda during the next few days as a large and powerful hurricane, bringing a risk of strong winds, heavy rainfall, and coastal flooding to the island by the middle of this week. Interests in Bermuda should closely monitor the latest forecast updates during the next few days, and tropical storm watches could be needed for the island as soon as tomorrow. FORECAST POSITIONS AND MAX WINDS INIT 07/0300Z 23.1N 54.4W 110 KT 125 MPH 12H 07/1200Z 24.1N 55.5W 105 KT 120 MPH 24H 08/0000Z 25.6N 56.8W 100 KT 115 MPH 36H 08/1200Z 27.3N 58.2W 95 KT 110 MPH 48H 09/0000Z 29.2N 59.9W 95 KT 110 MPH 60H 09/1200Z 31.6N 61.3W 90 KT 105 MPH 72H 10/0000Z 34.6N 61.8W 90 KT 105 MPH 96H 11/0000Z 44.0N 55.7W 80 KT 90 MPH 120H 12/0000Z 55.5N 43.4W 65 KT 75 MPH...POST-TROP/EXTRATROP $$ Forecaster Papin

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