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Tropical Storm Olaf Forecast Discussion Number 4
2021-09-08 16:40:59| National Hurricane Center (East Pacific)
Issued at 900 AM MDT Wed Sep 08 2021 000 WTPZ45 KNHC 081440 TCDEP5 Tropical Storm Olaf Discussion Number 4 NWS National Hurricane Center Miami FL EP152021 900 AM MDT Wed Sep 08 2021 The depression has strengthened into Tropical Storm Olaf this morning. A well-defined curved band now wraps over 50 percent around the center of the cyclone, with cloud tops to -80 degrees C. The initial intensity has been raised to 35 kt for this advisory based on the latest TAFB Dvorak intensity estimate and the UW-CIMSS ADT. Olaf is forecast to remain over warm waters and in a moist environment for the next 36 hours or so. The only inhibiting factor to strengthening in the short term could be a slight increase in vertical wind shear beginning tonight. In a couple of days, the cyclone is forecast to begin moving over cooler waters and into a drier, much more stable atmospheric environment that favors rapid weakening. These unfavorable conditions should cause Olaf to degenerate into a remnant low this weekend. The latest NHC intensity forecast was decreased only slightly from the previous one, and is in good agreement with the IVCN intensity consensus. Although the NHC forecast no longer explicitly shows Olaf becoming a hurricane, this could still occur Thursday or Thursday night. The storm is now moving northwestward at 6 kt, to the southwest of a mid-level ridge building over northern Mexico. This northwestward motion should continue for a couple of days with a gradual increase in forward speed. By Friday night, Olaf is expected to turn west-northwestward as it weakens, and by Saturday a westward motion is forecast as the cyclone becomes shallow and steered by the surrounding low-level flow. The latest NHC track forecast is little changed from the previous one, and lies near the various multi-model consensus tracks. It should be noted that the model solutions that depict a stronger cyclone favor a track slightly more to the north than the NHC forecast, closer to the southern Baja peninsula, while the weaker model solutions lie to the south of the NHC forecast track. Key Messages: 1. Olaf is forecast to strengthen to near hurricane intensity while it passes to the southwest of southern portions of Baja California Sur Thursday and Friday, and tropical storm conditions are possible in these areas. Interests there should continue to monitor the progress of Olaf. 2. Heavy rains associated with Olaf are possible across southern portions of Baja California Sur Thursday through Friday. This will pose a threat of flash flooding and mudslides. FORECAST POSITIONS AND MAX WINDS INIT 08/1500Z 18.9N 107.5W 35 KT 40 MPH 12H 09/0000Z 19.6N 108.0W 45 KT 50 MPH 24H 09/1200Z 20.6N 109.0W 55 KT 65 MPH 36H 10/0000Z 21.7N 110.5W 60 KT 70 MPH 48H 10/1200Z 22.9N 112.2W 55 KT 65 MPH 60H 11/0000Z 23.5N 113.9W 45 KT 50 MPH 72H 11/1200Z 23.8N 115.4W 35 KT 40 MPH 96H 12/1200Z 23.7N 118.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 120H 13/1200Z 23.0N 120.7W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Latto
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Hurricane Larry Forecast Discussion Number 31
2021-09-08 10:50:28| National Hurricane Center (Atlantic)
Issued at 500 AM AST Wed Sep 08 2021 000 WTNT42 KNHC 080850 TCDAT2 Hurricane Larry Discussion Number 31 NWS National Hurricane Center Miami FL AL122021 500 AM AST Wed Sep 08 2021 Larry's overall satellite presentation has not changed appreciably overnight, however there has been some recent cooling of the cloud tops in the surrounding ring of convection. A fairly recent AMSR2 microwave overpass has revealed a fragmented inner eye with a band or ring of convection at a fairly large radius from the center. Subjective Dvorak Current Intensity (CI) numbers from TAFB and SAB are T5.0 (90 kt) while objective UW/CIMSS ADT T-numbers are around T5.8 (110 kt). A consensus of these estimates, and the latest SATCON estimate of 100 kt, is used as the initial intensity for this advisory. The next Air Force Reserve Hurricane Hunter aircraft is scheduled to investigate Larry this morning and should provide in situ data to help better ascertain the intensity and structure of the hurricane. Larry continues to move northwestward or 325/9 kt. The track forecast reasoning is once again unchanged from before. Larry is expected to move northwestward and then northward around the western portion of a deep-layer ridge during the next 36 to 48 hours, with the center of the hurricane passing east of Bermuda on Thursday. After that time, Larry should begin to accelerate northeastward ahead of a deep-layer trough that will be moving across the northeastern United States, and this will bring the cyclone near or over southeastern Newfoundland in about 72 hours. The track guidance continues to be in excellent agreement, and only slight modifications were made to the previous official forecast. The updated NHC track is near the various consensus aids and the latest GFS ensemble mean. The hurricane is forecast to remain within an area of low vertical wind shear for the next day or two, but the upper-ocean heat content will be gradually decreasing along the forecast path. This, along with some upwelling beneath the relatively slow-moving hurricane, is likely to result in gradual weakening over the next couple of days. After that time, increasing southwesterly shear and much colder SSTs along the forecast track should result in additional weakening. The global models indicate that Larry will merge with a frontal zone and complete its extratropical transition in a little more than 3 days. The NHC intensity forecast is once again similar to the previous advisory and is in best agreement with the IVCN consensus aid. Key Messages: 1. Large swells generated by Larry will continue to affect the Leeward Islands, portions of the Greater Antilles, and the Bahamas today. Significant swells will begin to reach the east coast of the United States and Atlantic Canada later today 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 08/0900Z 26.5N 57.3W 100 KT 115 MPH 12H 08/1800Z 28.0N 58.7W 95 KT 110 MPH 24H 09/0600Z 30.1N 60.6W 95 KT 110 MPH 36H 09/1800Z 32.9N 61.9W 90 KT 105 MPH 48H 10/0600Z 36.7N 61.6W 85 KT 100 MPH 60H 10/1800Z 41.7N 58.3W 80 KT 90 MPH 72H 11/0600Z 47.3N 52.4W 75 KT 85 MPH 96H 12/0600Z 58.8N 40.0W 60 KT 70 MPH...POST-TROP/EXTRATROP 120H 13/0600Z 65.0N 33.0W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ Forecaster Brown
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Tropical Depression Fifteen-E Forecast Discussion Number 3
2021-09-08 10:49:33| National Hurricane Center (East Pacific)
Issued at 300 AM MDT Wed Sep 08 2021 000 WTPZ45 KNHC 080849 TCDEP5 Tropical Depression Fifteen-E Discussion Number 3 NWS National Hurricane Center Miami FL EP152021 300 AM MDT Wed Sep 08 2021 The circulation of the depression has continued to become better defined, and there has been a substantial increase in deep convection within bands to the north and northeast of the center. However, the inner core remains slightly displaced from this activity, and a combination of subjective and objective intensity estimates supports maintaining the cyclone as a 30-kt depression for this advisory. The system has either been meandering or its center re-formed yesterday, and the long-term motion is a drift toward the north-northwest (335 degrees) at about 3 kt. This motion is likely due to the depression being caught within weak steering currents between a mid-level low west of the Baja California peninsula and troughing extending across Mexico to the Gulf of Mexico. A strong mid-tropospheric high over the western United States should gradually cause the system to move faster toward the northwest during the next 2 to 3 days, bringing it very close to Baja California Sur in about 48 hours. Of the track models, the GFS and COAMPS-TC models are the solutions which bring the cyclone's center closest to Baja California Sur, while the ECMWF and UKMET models have the farther-offshore tracks. The new NHC track forecast splits the difference among these solutions and is a little east of the previous forecast during the first 36 hours to account for recent short-term motions. After 36 hours, it falls more or less in line with the previous prediction and is very close to the consensus aids, HWRF, and HMON. There are counteracting factors at play regarding the depression's future intensity. Although deep-layer shear is forecast to be low, the GFS suggests that moderate to strong mid-level shear could develop below the outflow level during the next 24-48 hours. Sea surface temperatures will be plenty warm for strengthening during the next 48 hours, yet upper-level divergence is not expected to be ideal. Since the system's circulation appears to be improving, steady strengthening is forecast during the first 48 hours, and the depression could become a short-lived hurricane while it passes the Baja California peninsula. This forecast is near the upper end of the guidance envelope, close to the GFS, HWRF, COAMPS-TC, and HCCA solutions. The cyclone will be moving over colder waters in 2-3 days, which should cause quick weakening and a degeneration to remnant low status by day 4. Key Messages: 1. Tropical Depression Fifteen-E is expected to strengthen to a tropical storm later today, and it could become a short-lived hurricane while it passes just to the southwest of southern portions of Baja California Sur Thursday and Friday. A Tropical Storm Watch is in effect for southern portions of Baja California Sur, and interests there should continue to monitor the progress of the depression. 2. Heavy rains associated with Tropical Depression Fifteen-E are possible across southern portions of Baja California Sur Thursday through Friday. This will pose a threat of flash flooding and mudslides. FORECAST POSITIONS AND MAX WINDS INIT 08/0900Z 18.5N 107.1W 30 KT 35 MPH 12H 08/1800Z 19.1N 107.6W 40 KT 45 MPH 24H 09/0600Z 20.0N 108.4W 50 KT 60 MPH 36H 09/1800Z 21.1N 109.6W 60 KT 70 MPH 48H 10/0600Z 22.3N 111.2W 65 KT 75 MPH 60H 10/1800Z 23.3N 112.8W 55 KT 65 MPH 72H 11/0600Z 23.9N 114.5W 45 KT 50 MPH 96H 12/0600Z 24.1N 117.1W 30 KT 35 MPH...POST-TROP/REMNT LOW 120H 13/0600Z 23.6N 119.6W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Berg
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Tropical Depression Fifteen-E Forecast Discussion Number 2
2021-09-08 04:43:53| National Hurricane Center (East Pacific)
Issued at 900 PM MDT Tue Sep 07 2021 000 WTPZ45 KNHC 080243 TCDEP5 Tropical Depression Fifteen-E Discussion Number 2 NWS National Hurricane Center Miami FL EP152021 900 PM MDT Tue Sep 07 2021 Satellite imagery indicates that Tropical Depression Fifteen-E has changed little in organization during the past several hours. While the system is producing good convective banding in the eastern semicircle, the convection near the center is currently poorly organized, and there is no evidence that the inner core has consolidated. Thus, the initial intensity remains 30 kt based mainly on continuity from the previous advisory. A combination of conventional and 37 GHz microwave satellite imagery suggests that the center is farther east than previously thought, so the new initial position is about a half degree east of the previous advisory position. The initial motion is a somewhat uncertain 300/5. A large mid-level anticyclone is located over the southwestern United States with a ridge extending southeastward across Mexico. The anticyclone should shift a little eastward during the next few days, with the ridge extending southward across Mexico. This evolution should steer the tropical cyclone generally northwestward for the next several days, followed by a more westward motion as the cyclone weakens over cooler water and is steered by low-level easterly flow. The track guidance is in good agreement with this scenario, and the new forecast track is near the consensus models. However, the more eastward initial position required an eastward shift to the forecast track. It should be noted that some erratic motion is possible until the cyclone develops a better-defined inner core. Conditions appear favorable for strengthening until the system reaches the 26-deg-C SST isotherm in 60-72 h, with the main restraining factor being the current lack of internal organization. The intensity forecast has only minor adjustments from the previous forecast and calls for the depression to become a tropical storm in about 12 h and a hurricane in about 48 h. Steady to rapid weakening is expected after 60-72 h due to the cooler water and dry air entrainment. The more easterly initial position and the new forecast track require a Tropical Storm Watch for portions of Baja California Sur at this time. Interests elsewhere in Baja California Sur should monitor the progress of this system. FORECAST POSITIONS AND MAX WINDS INIT 08/0300Z 18.2N 107.4W 30 KT 35 MPH 12H 08/1200Z 18.6N 107.7W 35 KT 40 MPH 24H 09/0000Z 19.4N 108.4W 45 KT 50 MPH 36H 09/1200Z 20.4N 109.2W 55 KT 65 MPH 48H 10/0000Z 21.7N 110.6W 65 KT 75 MPH 60H 10/1200Z 22.8N 112.0W 65 KT 75 MPH 72H 11/0000Z 23.7N 113.7W 55 KT 65 MPH 96H 12/0000Z 24.5N 116.5W 40 KT 45 MPH 120H 13/0000Z 24.0N 119.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Beven
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Hurricane Larry Forecast Discussion Number 30
2021-09-08 04:43:23| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Tue Sep 07 2021 000 WTNT42 KNHC 080243 TCDAT2 Hurricane Larry Discussion Number 30 NWS National Hurricane Center Miami FL AL122021 1100 PM AST Tue Sep 07 2021 Larry's eye has become a little better defined since the previous advisory, and the eyewall convective cloud tops have cooled, with a nearly solid ring of -65C to -70C now surrounding the eye. Data from an Air Force Reserve Hurricane Hunter aircraft indicate that the central pressure has risen slightly to 966-968 mb and that peak 700-mb flight-level winds measured were 106 kt in the northeast quadrant. These data would suggest that the intensity has decreased a little to 95-96 kt. However, the peak flight-level wind of 106 kt was measured in the wake of a strong eyewall convective burst, suggesting that stronger winds could have been present in that convection. Also, if the surrounding eyewall convective ring closes off during the nocturnal convective maximum period in another six hours, then Dvorak intensity estimates would increase from the current T5.0/90 kt to T5.5/102 kt. Thus, Larry's intensity has been maintained at 100 kt for this advisory in order to avoid possible intensity vacillations. The initial motion estimate is 325/10 kt, based on reconnaissance aircraft fixes over the past 12 hours. There remains no significant change to the track forecast or reasoning over the past 48 hours. The latest NHC model guidance remains in strong agreement on Larry continuing to move northwestward and then northward around the western periphery of a deep-layer subtropical ridge during the next 48 hours or so. After passing east of Bermuda by early day 3, the hurricane is forecast to accelerate northeastward and move into the mid-latitude westerlies ahead of a large, eastward-moving trough that is currently approaching the northeastern United States and Atlantic Canada. By day 5, Larry is expected to move across the far north Atlantic. The new NHC track forecast is similar to the previous advisory track, and lies along the eastern edge of the tightly packed simple- and corrected-consensus track models. Larry's upper-level outflow pattern remains impressive, and has even expanded and accelerated on the east side owing to a southward-digging upper-level trough, which has enhanced the outflow in that part of the hurricane. The vertical wind shear affecting Larry is expected to remain low for the next 24 hours or so while the hurricane passes over even warmer sea-surface temperatures (SST) approaching 29.7 deg C, even though the oceanic heat content will be decreasing. However, entrainment of dry mid-level air along with eye fluctuations are expected to offset the warmer SSTs. Thus, a slow but steady decrease in intensity through 48-60 hours is expected. Late in the forecast period, colder waters and increasing southwesterly vertical wind shear exceeding 30 kt should induce a faster rate of weakening. By 96-120 hours, the global models also indicate Larry will be merging with a frontal zone. Therefore, the new intensity forecast continues to show extratropical transition during that time period. The official intensity forecast is similar to the previous advisory, and closely follows the simple- and corrected-consensus intensity models IVCN and NOAA-HCCA. 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 08/0300Z 25.8N 56.8W 100 KT 115 MPH 12H 08/1200Z 27.2N 58.0W 95 KT 110 MPH 24H 09/0000Z 29.2N 59.6W 95 KT 110 MPH 36H 09/1200Z 31.5N 61.3W 90 KT 105 MPH 48H 10/0000Z 34.6N 61.8W 90 KT 105 MPH 60H 10/1200Z 39.1N 60.1W 85 KT 100 MPH 72H 11/0000Z 44.5N 55.7W 80 KT 90 MPH 96H 12/0000Z 56.2N 43.6W 65 KT 75 MPH...POST-TROP/EXTRATROP 120H 13/0000Z 62.8N 33.6W 50 KT 60 MPH...POST-TROP/EXTRATROP $$ Forecaster Stewart
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