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Tropical Storm Larry Forecast Discussion Number 4

2021-09-01 16:50:32| National Hurricane Center (Atlantic)

Issued at 200 PM CVT Wed Sep 01 2021 000 WTNT42 KNHC 011450 TCDAT2 Tropical Storm Larry Discussion Number 4 NWS National Hurricane Center Miami FL AL122021 200 PM CVT Wed Sep 01 2021 Satellite imagery this morning shows that Larry is becoming better organized, with curved convective bands increasing around the center. Various subjective and objective satellite intensity estimates were in the 35-55 kt range around 12Z, and ASCAT data near the time showed 40 kt winds. Based on increasing organization since that time, the initial intensity is increased to 45 kt. Larry is moving quickly westward, although there is some uncertainty in the forward speed due to the possibility the center re-formed during the night. The best estimate of the motion is 270/19 kt. As noted in the previous advisory, the cyclone is expected to move around the southern and southwestern periphery of the sprawling Bermuda-Azores ridge for the next 5 days, resulting in a general west motion for 24-36 h, followed by a turn toward the west-northwest and, by 96-120 h, a turn toward the northwest. After 36 h, there is some spread in the track guidance, with the GFS generally on the right side of the guidance envelope and the UKMET on the left side, a spread often seen for westward-moving cyclones south of the Bermuda-Azores high. Due to a more westerly initial position, the guidance has shifted a little more to the west, and the new forecast track is again shifted to the west of the previous track. The new forecast lies a little to the south of the various consensus models. Conditions appear favorable for steady to rapid strengthening during the next 48-60 h due to light shear, a moist environment, and sea surface temperatures of 27-28C along the forecast track. The new intensity forecast calls for Larry to become a hurricane in about 24 h and a major hurricane near 60 h. After that time, the global models suggest the possibility of dry air entrainment, and by 120 h there is likely to be moderate westerly shear over the cyclone. Based on this forecast environment and the guidance trends, the intensity forecast calls for little change in strength from 72-120 h. The new intensity forecast lies near the upper edge of the intensity guidance. FORECAST POSITIONS AND MAX WINDS INIT 01/1500Z 12.3N 27.6W 45 KT 50 MPH 12H 02/0000Z 12.4N 30.4W 55 KT 65 MPH 24H 02/1200Z 12.7N 33.4W 65 KT 75 MPH 36H 03/0000Z 13.2N 36.5W 75 KT 85 MPH 48H 03/1200Z 13.9N 39.2W 90 KT 105 MPH 60H 04/0000Z 15.0N 41.9W 100 KT 115 MPH 72H 04/1200Z 16.2N 44.6W 105 KT 120 MPH 96H 05/1200Z 19.0N 49.5W 105 KT 120 MPH 120H 06/1200Z 22.0N 52.5W 105 KT 120 MPH $$ Forecaster Beven

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Tropical Storm Larry Forecast Discussion Number 3

2021-09-01 10:59:00| National Hurricane Center (Atlantic)

Issued at 800 AM CVT Wed Sep 01 2021 000 WTNT42 KNHC 010858 TCDAT2 Tropical Storm Larry Discussion Number 3 NWS National Hurricane Center Miami FL AL122021 800 AM CVT Wed Sep 01 2021 Deep convection with cloud tops colder than -80C have increased over and to the west of the low-level center since the previous advisory. Subjective satellite intensity estimates at 0600 UTC from TAFB and SAB were T2.5/35 kt and T3.0/45 kt, while the most recent objective intensity estimates from UW-CIMSS are T2.8/41 kt from ADT and 37 kt from SATCON. An average of these intensity estimates support increasing the advisory intensity to 40 kt, making the cyclone Tropical Storm Larry. In addition, 0300 UTC and 0700 UTC observations from ship VRNF3, which recently passed through the center of Larry, reported a pressure of 1006.8 mb and winds near 25 kt. These data were the basis for the estimated central pressure of 1003 mb, a pressure value that also supports an intensity of 40 kt. Larry has turned more westward over the past several hours, and the new motion estimate is 280/17 kt. Larry is expected to move around the southern and southwestern periphery of the sprawling Bermuda-Azores ridge for the next 5 days, resulting in a general west motion for the next 36 hours or so, followed by a turn toward the west-northwest on Friday, and a northwestward motion over the weekend and continuing into early next week. There has been a pronounced westward shift in the track guidance for this cycle, with the greatest shift coming from the GFS model. Over the past 36 hours, the GFS has shifted its track westward by more than 500 nmi, and even the latest shift still keeps the GFS model the easternmost track forecast in the guidance suite. In contrast, the ECMWF and UKMET models, which lie along the westernmost portion of the guidance envelope, have been fairly stable. Owing to the westward shift in the overall guidance envelope, and considering the GFS solution as an outlier model, the new NHC forecast track has also been shifted westward, and lies between the NOAA-HCCA corrected-consensus model to the south, and the tightly packed TVCA simple-consensus model and FSSE corrected-consensus model to the north. Given the poor handling of the ridge to the north of Larry by the GFS, subsequent NHC forecast tracks may have to be shifted farther west. Given the improved inner-core wind field based on earlier ASCAT wind data and reports from ship VRNF3, along with warm sea-surface temperatures of 28 deg C and light easterly to southeasterly vertical shear of around 5 kt, steady strengthening is expected for the next 24 hours or so. By 36 hours when Larry is expected to be a hurricane and have a well-established and tighter inner-core wind field and possibly an eye, rapid intensification is forecast, with Larry becoming a major hurricane by 72 hour. This in large part due to the massive equatorward upper-level outflow pattern that all of the global and regional models are forecasting, which is the same type of outflow pattern that recently occurred with Hurricane Ida. The new official intensity forecast is above the previous advisory forecast by about 10 kt at all forecast times, and conservatively follows an average of the Decay-SHIPS, COAMPS-TC, FSSE, and ECMWF models. This intensity forecast is near the upper end of the guidance envelope and is above the other consensus intensity models. FORECAST POSITIONS AND MAX WINDS INIT 01/0900Z 12.3N 24.8W 40 KT 45 MPH 12H 01/1800Z 12.5N 27.5W 50 KT 60 MPH 24H 02/0600Z 12.6N 30.6W 60 KT 70 MPH 36H 02/1800Z 13.1N 33.7W 70 KT 80 MPH 48H 03/0600Z 13.6N 36.8W 85 KT 100 MPH 60H 03/1800Z 14.4N 39.7W 95 KT 110 MPH 72H 04/0600Z 15.5N 42.0W 100 KT 115 MPH 96H 05/0600Z 18.2N 46.9W 105 KT 120 MPH 120H 06/0600Z 21.3N 50.6W 105 KT 120 MPH $$ Forecaster Stewart

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Tropical Depression Kate Forecast Discussion Number 17

2021-09-01 10:33:59| National Hurricane Center (Atlantic)

Issued at 500 AM AST Wed Sep 01 2021 000 WTNT45 KNHC 010833 TCDAT5 Tropical Depression Kate Discussion Number 17 NWS National Hurricane Center Miami FL AL102021 500 AM AST Wed Sep 01 2021 After the earlier convective hiatus, a concentrated area of thunderstorm activity containing numerous lightning strikes has developed over and to the east of the low-level center. In addition, upper-level outflow has been expanding to the west, an indication that the hostile shear conditions that have been plaguing the cyclone the past few days has finally waned. ASCAT data around 0000-0100Z showed peak winds near 25 kt; however, the recent sharp increase in deep convection along with a consensus Dvorak subjective intensity of T2.0/30 kt supports increasing the intensity to 30 kt. The 30-kt advisory intensity is also supported by UW-CIMSS objective intensity estimates of T2.1/31 kt from ADT and 39 kt from SATCON. The initial motion estimate is 340/08 kt. Kate is moving north-northwestward between a small mid- to upper-level low to the south of the cyclone and deep-layer ridge located to the north and east of the system. A gradual turn toward the northwest is expected later today, followed by a turn back toward the north on Thursday as Kate rounds the western periphery of the ridge. By Friday, recurvature toward the north-northeast and northeast into the mid-latitude westerlies is forecast when the cyclone will be lifted out by an eastward-moving deep-layer trough currently crossing the western Atlantic. The new NHC track forecast is similar to but a little to the left of the previous advisory track, and closely follows the tightly packed consensus track forecast models TVCA and NOAA-HCCA. A 0505 UTC AMSR-2 microwave pass revealed that Kate's compact circulation had tightened up considerably since the earlier 0100 UTC ASCAT wind data, which shows a broad and elongated inner-core wind field. Also, Kate is currently passing between two small upper-level lows to the north and south of the cyclone, which is aiding the upper-level divergence across the system, albeit somewhat constrained due to the short distance of only about 300 nmi between the two upper lows. Given the locally enhanced outflow and the recent increase in deep convection, it s not out of the question that Kate could restrengthen back into a low-end tropical storm during the next 24 hours or so. However, the entrainment of dry mid-level air with humidity values less than 50 percent should prevent any significant or rapid restrengthening from occuring. by 48 hours, moderate northerly shear and even drier mid-level air should cause convection weaken, resulting in a gradual spin down of the circulation and eventual dissipation by 72 hours. The new NHC intensity forecast is similar to but slightly lower than the consensus intensity models IVCN and HCCA, and the Decay-SHIPS statistical-dynamical intensity model. FORECAST POSITIONS AND MAX WINDS INIT 01/0900Z 25.7N 51.7W 30 KT 35 MPH 12H 01/1800Z 26.9N 52.5W 30 KT 35 MPH 24H 02/0600Z 28.5N 53.2W 30 KT 35 MPH 36H 02/1800Z 30.3N 53.7W 25 KT 30 MPH 48H 03/0600Z 31.9N 53.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 60H 03/1800Z 33.5N 53.1W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 04/0600Z...DISSIPATED $$ Forecaster Stewart

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Tropical Depression Kate Forecast Discussion Number 16

2021-09-01 04:33:26| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Tue Aug 31 2021 000 WTNT45 KNHC 010233 TCDAT5 Tropical Depression Kate Discussion Number 16 NWS National Hurricane Center Miami FL AL102021 1100 PM AST Tue Aug 31 2021 Some bursts of convection have been forming within Kate's small circulation during the past several hours, but none of it has any real significant organization. In addition, the low clouds appear to be losing definition, and a very-recent ASCAT-B pass showed that the maximum winds are now only about 25 kt. It's going to be difficult for Kate to make much of a comeback, if at all. Moderate northerly shear, dry mid-level air, upper-level convergence, and an increasingly anticyclonic low-level environment are likely to cause the circulation to spin down further and make it hard for deep convection to persist. Therefore, the NHC official forecast now calls for additional weakening, with Kate likely becoming a remnant low by 36 hours (if not sooner) and dissipating by 72 hours. This scenario is closest to the GFS, HWRF, and HMON solutions. Located on the southwestern periphery of a low-level area of high pressure, Kate is moving toward the north-northwest (345/9 kt). The depression is forecast to turn toward the northwest by morning, but then recurve around the high toward the north and north-northeast in a couple of days. The NHC track forecast remains close to the consensus aids and is generally just an update from the previous advisory. FORECAST POSITIONS AND MAX WINDS INIT 01/0300Z 25.4N 51.3W 25 KT 30 MPH 12H 01/1200Z 26.4N 52.1W 25 KT 30 MPH 24H 02/0000Z 27.9N 53.1W 25 KT 30 MPH 36H 02/1200Z 29.8N 53.8W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 03/0000Z 31.6N 54.1W 20 KT 25 MPH...POST-TROP/REMNT LOW 60H 03/1200Z 33.1N 53.7W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 04/0000Z...DISSIPATED $$ Forecaster Berg

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Tropical Depression Twelve Forecast Discussion Number 2

2021-09-01 04:32:25| National Hurricane Center (Atlantic)

Issued at 200 AM CVT Wed Sep 01 2021 000 WTNT42 KNHC 010232 TCDAT2 Tropical Depression Twelve Discussion Number 2 NWS National Hurricane Center Miami FL AL122021 200 AM CVT Wed Sep 01 2021 Satellite images indicate that the depression is gradually becoming better organized. An area of deep convection has been persisting near the center, and banding features are beginning to take shape. The latest Dvorak estimates from TAFB and SAB have increased to 2.5/35 kt, which would support upgrading the system to a tropical storm. However, a recent ASCAT-B overpass around 2300 UTC showed maximum winds in the 25-30 kt range in the northeastern quadrant, and based on that data the initial intensity is held at 30 kt. The tropical depression is moving fairly quickly to the west-northwest at 17 kt. The track forecast reasoning appears fairly straightforward. The cyclone is expected to move at a relatively fast pace to the west or west-northwest during the next couple of days as it remains on the south side of a strong mid-level ridge. After that time, a decrease in forward speed and a gradual turn to the northwest are expected as the system nears the southwestern side of the ridge. Although most of the models agree on the synoptic steering pattern, there is a fair amount of spread from days 3 to 5 in how soon the northwestward turn will occur. The NHC track forecast lies near the middle of the guidance envelope and is a little to the north of the previous one based on the more poleward initial position. Since the system is expected to be over relatively warm water and in an air mass of low wind shear and abundant moisture, steady strengthening is expected during the next couple of days. The depression is likely to become a tropical storm within the next 12 hours and a hurricane in 36 to 48 hours. Beyond a few days, an increase in shear and drier air should slow the rate of intensification. The NHC intensity forecast follows the trend of the HCCA, IVCN, and IVDR models. In addition, the global models all show the cyclone becoming fairly large toward the end of the forecast period. The NHC forecast wind radii is larger than the previous one, trending toward the radii consensus aid. FORECAST POSITIONS AND MAX WINDS INIT 01/0300Z 12.1N 23.2W 30 KT 35 MPH 12H 01/1200Z 12.6N 25.9W 40 KT 45 MPH 24H 02/0000Z 12.8N 29.2W 50 KT 60 MPH 36H 02/1200Z 13.2N 32.1W 60 KT 70 MPH 48H 03/0000Z 13.8N 35.1W 70 KT 80 MPH 60H 03/1200Z 14.5N 37.5W 80 KT 90 MPH 72H 04/0000Z 15.4N 40.1W 85 KT 100 MPH 96H 05/0000Z 18.0N 44.5W 90 KT 105 MPH 120H 06/0000Z 20.7N 47.9W 95 KT 110 MPH $$ Forecaster Cangialosi

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