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Tropical Storm Carlos Forecast Discussion Number 8

2021-06-14 16:50:49| National Hurricane Center (East Pacific)

Issued at 800 AM PDT Mon Jun 14 2021 000 WTPZ43 KNHC 141432 TCDEP3 Tropical Storm Carlos Discussion Number 8 NWS National Hurricane Center Miami FL EP032021 800 AM PDT Mon Jun 14 2021 After being nearly devoid of deep convection for much of the night, a new burst of convection has redeveloped near the center of the cyclone's circulation. A blend of the latest Dvorak T-numbers from TAFB and SAB support maintaining an initial intensity of 35 kt for this advisory. Carlos is moving west-southwest at 7 kt, steered by a low- to mid-level ridge to its north. Most of the track guidance is now in good agreement on keeping this ridge intact over the next several days, forcing Carlos on the same west-southwest trajectory for the next day or so, followed by a gradual turn to the west by midweek. The latest NHC track forecast is near the previous one through 48 h, and a little faster and south of it beyond that time. Most guidance remains to the left of the latest NHC forecast, so additional adjustments may be required later today. Satellite images show a vast area of dry and stable air to the north and west of Carlos, with stratocumulus being drawn into the western portion of the cyclone's circulation. This undoubtedly helped to contribute to the sputtering of convective activity overnight. The ongoing intrusions of dry, stable air should continue to periodically disrupt the development of deep convection over the next day or so, which should cause Carlos to slowly weaken. By 36-48 h, southwesterly vertical wind shear in excess of 20 kt is expected to hasten the weakening process, resulting in Carlos degenerating into a remnant low by midweek. Thereafter, only sporadic convection is expected to develop in association with the remnant low as it gradually spins down. The latest NHC intensity forecast is nearly the same as the previous one and is in agreement with the bulk of the guidance. FORECAST POSITIONS AND MAX WINDS INIT 14/1500Z 11.3N 128.6W 35 KT 40 MPH 12H 15/0000Z 10.9N 129.6W 30 KT 35 MPH 24H 15/1200Z 10.6N 130.9W 30 KT 35 MPH 36H 16/0000Z 10.3N 132.3W 25 KT 30 MPH 48H 16/1200Z 10.2N 133.6W 25 KT 30 MPH...POST-TROP/REMNT LOW 60H 17/0000Z 10.2N 134.7W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 17/1200Z 10.3N 135.8W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 18/1200Z 10.7N 137.4W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 19/1200Z 11.1N 139.0W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Latto

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Tropical Storm Carlos Forecast Discussion Number 7

2021-06-14 10:36:04| National Hurricane Center (East Pacific)

Issued at 200 AM PDT Mon Jun 14 2021 000 WTPZ43 KNHC 140835 TCDEP3 Tropical Storm Carlos Discussion Number 7 NWS National Hurricane Center Miami FL EP032021 200 AM PDT Mon Jun 14 2021 The satellite presentation of Carlos has continued to erode early this morning, with only three remnant convective cells noted rotating around the center. As a result, subjective and objective satellite intensity estimates have fallen sharply. Thus, the initial intensity has also been lowered to 35 kt, which could be generous. The initial motion estimate is 255/06 kt. Carlos is forecast by the global and regional models to be steered west-southwestward to westward throughout the 5-day period by a strong low- to mid-level subtropical ridge situated to its north and northwest. The latest model guidance has come into much better agreement on this track scenario, especially compared to this time yesterday, and the new NHC track forecast follows suit and lies close to a blend of the HCCA and TVCE consensus track models. Although sea-surface temperatures are expected to remain warm enough to support a tropical cyclone, the continued ingestion of cooler, drier, and more stable air that now completely surrounds Carlos is forecast to continue to erode the central deep convection, with the cyclone weakening a tropical depression later today. By 36-48h, southwesterly vertical wind shear in excess of 20 kt is expected to hasten the weakening process, resulting in Carlos degenerating into a remnant low. Although there will likely be periodic short-lived bursts of convection, especially at night, the general trend should be gradual weakening throughout the 120-h forecast period, perhaps even faster than indicated by the official intensity forecast. FORECAST POSITIONS AND MAX WINDS INIT 14/0900Z 11.4N 127.8W 35 KT 40 MPH 12H 14/1800Z 11.2N 128.5W 30 KT 35 MPH 24H 15/0600Z 10.8N 129.6W 30 KT 35 MPH 36H 15/1800Z 10.4N 130.8W 25 KT 30 MPH 48H 16/0600Z 10.2N 132.1W 25 KT 30 MPH...POST-TROP/REMNT LOW 60H 16/1800Z 10.2N 133.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 17/0600Z 10.5N 134.4W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 18/0600Z 11.0N 136.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 19/0600Z 11.5N 137.6W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Stewart

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Tropical Storm Carlos Forecast Discussion Number 6

2021-06-14 04:38:25| National Hurricane Center (East Pacific)

Issued at 800 PM PDT Sun Jun 13 2021 000 WTPZ43 KNHC 140238 TCDEP3 Tropical Storm Carlos Discussion Number 6 NWS National Hurricane Center Miami FL EP032021 800 PM PDT Sun Jun 13 2021 The satellite appearance of Carlos has degraded this evening. A ragged area of deep convection persists near and to the west of the estimated center position, but infrared cloud top temperatures have recently warmed and the system's organization has not improved. Therefore, the initial intensity of Carlos is lowered to 40 kt for this advisory. This is consistent with objective UW-CIMSS ADT and SATCON estimates between 35-40 kt, as well as an average of the subjective Dvorak classifications received from TAFB and SAB. Carlos continues to be steered west-southwestward by a mid-level ridge to its north and northwest. This general motion is expected to persist for the next couple of days. Fortunately, the vast majority of reliable track guidance has come into much better agreement for day 3 and beyond, showing the weakening cyclone moving generally westward to the south of a low-level ridge. Substantial adjustments were once again made to the official NHC track forecast beyond 48 h to show a westward to west-northwestward motion on days 3-5, which is consistent with the latest guidance consensus. The updated track forecast lies closer to the HFIP corrected consensus approach (HCCA) and TVCE consensus aids, although it is still somewhat slower and right-of-track to allow for a gradual shift in the NHC forecast. Carlos is forecast to move over warm sea-surface temperatures in an environment with fairly low vertical wind shear for the next 12 h or so. However, surrounding dry air may periodically disrupt the cyclone's convective structure, and thus limit its ability to become more organized and intensify. Therefore, only small fluctuations in intensity are expected. Thereafter, decreasing oceanic heat content and increasing southwesterly vertical wind shear within a drier mid-level environment should induce a weakening trend. The latest NHC forecast calls for Carlos to weaken into a tropical depression by Tuesday night. Marginal environmental conditions and continued bouts of dry air will affect Carlos through late week, and it is plausible that Carlos will become a remnant low even earlier than forecast, perhaps by the end of the forecast period. FORECAST POSITIONS AND MAX WINDS INIT 14/0300Z 11.6N 127.1W 40 KT 45 MPH 12H 14/1200Z 11.3N 127.9W 40 KT 45 MPH 24H 15/0000Z 10.9N 128.9W 35 KT 40 MPH 36H 15/1200Z 10.5N 130.2W 35 KT 40 MPH 48H 16/0000Z 10.2N 131.6W 30 KT 35 MPH 60H 16/1200Z 10.2N 132.6W 30 KT 35 MPH 72H 17/0000Z 10.3N 133.7W 25 KT 30 MPH 96H 18/0000Z 11.0N 135.0W 25 KT 30 MPH 120H 19/0000Z 11.5N 136.5W 25 KT 30 MPH $$ Forecaster Reinhart/Pasch

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Tropical Storm Carlos Forecast Discussion Number 5

2021-06-13 22:38:21| National Hurricane Center (East Pacific)

Issued at 200 PM PDT Sun Jun 13 2021 000 WTPZ43 KNHC 132038 TCDEP3 Tropical Storm Carlos Discussion Number 5 NWS National Hurricane Center Miami FL EP032021 200 PM PDT Sun Jun 13 2021 Deep convection has managed to persist over the center of Carlos throughout the day today, although the appearance of this convection has become more ragged as the day has progressed. The blended CI values from TAFB and SAB suggest the system still has an intensity of 45 kt. A recent ASCAT overpass only partially captured the circulation with peak wind vectors of 39 kt. Compensating for possible undersampling by the instrument over only a portion of such a compact cyclone, maintaining 45 kt seems reasonable for the initial advisory intensity. Dry and stable air lies just to the north and west of Carlos, and occasional intrusions of this air into the cyclone's circulation could disrupt convection. However, the overnight diurnal convective maximum could overcome these intrusions over the next couple of nights. Therefore, only slight weakening is indicated through that time period. By 48 h, Carlos is expected to move into the stable airmass which should further disrupt its convection, causing additional weakening. By late in the forecast period the cyclone is forecast to be near or have crossed the 26 degree C SST isotherm. This should cause any remaining convection to gradually dissipate. Although not shown in the official forecast, it is possible Carlos will degenerate into a remnant low by the end of the forecast period, as suggested by the GFS. The latest NHC intensity forecast is very near the various multi-model consensus solutions. Carlos is beginning to show signs of slowing and turning to the left, with the initial motion now 260/6 kt. Model guidance remains in good agreement through 48 h, with the storm slowing and turning west-southwest as a mid-level ridge becomes oriented SW-NE to the north of the cyclone. There is still a vast amount of track guidance spread beyond 72 h, but not as much as earlier today. The GFS, which continues to be the easternmost solution has shifted well west of its previous track, showing Carlos turning northwest in a few days in response to a building ridge to its east, and weakening ridge to the north. The remaining guidance maintains the ridge to the north and shows Carlos turning west by midweek, then west-northwest by late this week. The official NHC forecast is near the previous one through 48 h. Beyond 48 h, large adjustments were required to accommodate the continuing westward trends in the guidance. Despite the abrupt shift in the official forecast for the latter half of the period, it remains well east of the consensus and the majority of available track guidance. FORECAST POSITIONS AND MAX WINDS INIT 13/2100Z 11.7N 126.6W 45 KT 50 MPH 12H 14/0600Z 11.4N 127.4W 40 KT 45 MPH 24H 14/1800Z 11.0N 128.3W 40 KT 45 MPH 36H 15/0600Z 10.6N 129.2W 40 KT 45 MPH 48H 15/1800Z 10.4N 130.0W 35 KT 40 MPH 60H 16/0600Z 10.3N 130.8W 30 KT 35 MPH 72H 16/1800Z 10.3N 131.3W 30 KT 35 MPH 96H 17/1800Z 10.7N 132.0W 25 KT 30 MPH 120H 18/1800Z 11.4N 132.7W 25 KT 30 MPH $$ Forecaster Latto

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Tropical Storm Carlos Forecast Discussion Number 4

2021-06-13 16:48:16| National Hurricane Center (East Pacific)

Issued at 800 AM PDT Sun Jun 13 2021 000 WTPZ43 KNHC 131448 TCDEP3 Tropical Storm Carlos Discussion Number 4 NWS National Hurricane Center Miami FL EP032021 800 AM PDT Sun Jun 13 2021 Deep convection has persisted over the center of Carlos throughout the night and a new convective burst with cloud tops of -60 to -70 degrees C is occuring over the estimated center location. A blend of the latest Dvorak intensity estimates from TAFB and SAB support increasing the initial intensity to 45 kt. This seems reasonable, as an earlier ASCAT-B overpass had several vectors of 40-41 kt, and the vortex likely has spun up further due to the ongoing deep convection. Carlos continues to move west at around 7 kt, steered by a mid-level ridge to the north. This ridge is forecast to become oriented northeast to southwest later today and prevail over the next couple days which should cause the cyclone to move slowly west-southwestward. After 48 h the models diverge significantly in their track solutions, with the GFS and ECMWF turning the system abruptly northward, while most of the other guidance has a more westward then west-northwestward motion beyond 72 h. There is a mid- to upper-level low currently located west of Mexico that the models are handling differently. The easternmost track solutions for Carlos weaken this feature more quickly and replace it with a ridge to the east of Carlos, while the western solutions keep the feature around, delaying the more poleward motion of the cyclone. The latest NHC track forecast is near the previous one through 48 h, but is shifted west thereafter. Still, the NHC forecast track is well east of the consensus after 48 h. Needless to say the track forecast confidence beyond day 2 is low. Northerly shear of 10-15 kt and the proximity to dry and stable mid-level air to its north should cause periodic weakening of the storm's deep convection, which would prevent any further strengthening, and Carlos is expected to hold its current intensity for the next couple of days. Thereafter, regardless of the western or eastern track model solutions, Carlos is expected to encounter an even drier and more stable airmass and cooler sea surface temperatures. This should cause a weakening trend to begin by mid-week. The latest NHC intensity forecast is little changed from the previous one, and is close to the multi-model consensus. FORECAST POSITIONS AND MAX WINDS INIT 13/1500Z 11.8N 126.0W 45 KT 50 MPH 12H 14/0000Z 11.6N 126.7W 45 KT 50 MPH 24H 14/1200Z 11.1N 127.5W 45 KT 50 MPH 36H 15/0000Z 10.7N 128.0W 45 KT 50 MPH 48H 15/1200Z 10.4N 128.5W 45 KT 50 MPH 60H 16/0000Z 10.4N 129.0W 40 KT 45 MPH 72H 16/1200Z 11.0N 129.4W 35 KT 40 MPH 96H 17/1200Z 12.8N 129.6W 30 KT 35 MPH 120H 18/1200Z 15.2N 129.4W 30 KT 35 MPH $$ Forecaster Latto

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