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Tropical Storm Kevin Forecast Discussion Number 13

2021-08-10 16:40:24| National Hurricane Center (East Pacific)

Issued at 900 AM MDT Tue Aug 10 2021 000 WTPZ41 KNHC 101440 TCDEP1 Tropical Storm Kevin Discussion Number 13 NWS National Hurricane Center Miami FL EP112021 900 AM MDT Tue Aug 10 2021 Kevin remains a sheared tropical cyclone, with the bulk of the deep convection located southwest of its center, while the center itself was exposed for a few hours earlier this morning. The structure of the cyclone has changed little since yesterday, and remains somewhat elongated. The estimated initial intensity is being held at 40 kt, using a blend of the latest Dvorak T-numbers from TAFB and SAB. Kevin continues to make its jog to the northwest, and the initial motion is 315/08 kt. A general northwestward to west-northwestward motion is expected over the next several days as Kevin moves along the southwestern periphery of a deep-layer ridge. Model guidance has continued to make a gradual shift to the north for the past several runs, and thus the latest NHC track forecast has been nudged a little northward as well, lying just south of the consensus models. Moderate to strong northeasterly wind shear is forecast to persist over Kevin for the next 24 h, which should limit the cyclone's ability to strengthen despite favorable SSTs and abundant mid-level moisture. By 24 h, the cyclone will begin to pass over progressively cooler waters and into a drier, more stable environment. Based on this scenario, the latest NHC intensity forecast shows no change in strength through much of tonight, followed by weakening beginning Wednesday morning. By 72 h, CMC and ECMWF model simulated satellite imagery suggest that Kevin will be devoid of organized convection, and so the official NHC forecast shows Kevin as a remnant low by that time. FORECAST POSITIONS AND MAX WINDS INIT 10/1500Z 19.1N 114.3W 40 KT 45 MPH 12H 11/0000Z 19.9N 115.2W 40 KT 45 MPH 24H 11/1200Z 21.0N 116.7W 35 KT 40 MPH 36H 12/0000Z 22.1N 118.4W 30 KT 35 MPH 48H 12/1200Z 23.1N 120.5W 25 KT 30 MPH 60H 13/0000Z 24.1N 122.8W 25 KT 30 MPH 72H 13/1200Z 25.2N 125.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 14/1200Z 27.2N 128.8W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 15/1200Z 28.7N 131.8W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Latto

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Tropical Depression Twelve-E Forecast Discussion Number 2

2021-08-10 16:39:12| Tropical Depression LIDIA

Issued at 1000 AM CDT Tue Aug 10 2021

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Potential Tropical Cyclone Six Forecast Discussion Number 3

2021-08-10 10:50:31| National Hurricane Center (Atlantic)

Issued at 500 AM AST Tue Aug 10 2021 000 WTNT41 KNHC 100850 TCDAT1 Potential Tropical Cyclone Six Discussion Number 3 NWS National Hurricane Center Miami FL AL062021 500 AM AST Tue Aug 10 2021 The disturbance moved through the southern Leeward Islands a few hours ago. Based on surface observations from the islands, the system still does not have a well-defined circulation. Although the satellite appearance shows some increase in organization, the surface data suggest no significant strengthening has occurred thus far. The current intensity estimate is held at 30 kt in agreement with a Dvorak estimate from SAB. A NOAA Hurricane Hunter aircraft is scheduled to investigate the disturbance later this morning and should provide an updated intensity estimate, and also determine whether the system has become a tropical cyclone. The disturbance continues moving west-northwestward, or about 295/15 kt. The flow on the south side of a strong subtropical ridge should maintain the west-northwestward track for the next 72 hours or so, with some slowing of forward speed by midweek. Beyond that time, a turn toward the northwest with further deceleration is likely while the system moves near the western periphery of the ridge. The official track forecast is very similar to the previous one and in good agreement with the latest simple and corrected multi-model consensus tracks. Users are reminded that the average track errors at days 4 and 5 are 175 miles and 200 miles, respectively. Dynamical conditions appear to be conducive for intensification during the next 24 hours or so, with low vertical shear and pronounced upper-level outflow over the system. The main hindrance for strengthening today and tonight appears to be some dry mid-tropospheric air in the environment, as shown by the global models. Since the projected track takes the disturbance or cyclone over the mountainous land mass of Hispaniola, some weakening and disruption of the circulation is likely in 36 hours or so. Later in the forecast period, the dynamical guidance shows some increase in westerly shear which could also inhibit strengthening. The official intensity forecast closely follows the NOAA corrected consensus forecast technique, HCCA. There is significant uncertainty in 4-5 day intensity forecasts, however. KEY MESSAGES: 1. The system is forecast to become a tropical storm as it moves over the northeastern Caribbean Sea today. Tropical storm conditions are expected in portions of the U.S. Virgin Islands and Puerto Rico beginning this afternoon, and in the Dominican Republic by Wednesday. Tropical storm conditions are possible in northern Haiti and the southeastern Bahamas by late Wednesday. 2. Heavy rainfall could lead to flash, urban, and small stream flooding and potential mudslides across the U.S. Virgin Islands and Puerto Rico. The greatest threat for flooding impacts will be across the eastern and southeastern portions of Puerto Rico. 3. There is a risk of wind and rainfall impacts elsewhere in portions of Hispaniola, the Bahamas, and Cuba later this week, although the forecast is more uncertain than usual since the system is still in its formative stage. Interests in these areas should monitor the system's progress and updates to the forecast. 4. Interests in the remainder of the Bahamas and Florida should monitor updates to the forecast for this system, but it is too soon to determine what if any impacts could occur there by late this week or this weekend given the uncertainty in the long-range forecast. FORECAST POSITIONS AND MAX WINDS INIT 10/0900Z 15.7N 62.2W 30 KT 35 MPH...POTENTIAL TROP CYCLONE 12H 10/1800Z 16.7N 64.6W 40 KT 45 MPH...TROPICAL CYCLONE 24H 11/0600Z 17.9N 67.4W 45 KT 50 MPH 36H 11/1800Z 19.0N 70.1W 30 KT 35 MPH...INLAND 48H 12/0600Z 20.1N 72.6W 30 KT 35 MPH 60H 12/1800Z 21.1N 74.9W 30 KT 35 MPH 72H 13/0600Z 22.0N 77.0W 35 KT 40 MPH 96H 14/0600Z 24.4N 80.8W 40 KT 45 MPH 120H 15/0600Z 26.8N 83.1W 50 KT 60 MPH $$ Forecaster Pasch

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Tropical Storm Kevin Forecast Discussion Number 12

2021-08-10 10:45:05| National Hurricane Center (East Pacific)

Issued at 300 AM MDT Tue Aug 10 2021 000 WTPZ41 KNHC 100844 TCDEP1 Tropical Storm Kevin Discussion Number 12 NWS National Hurricane Center Miami FL EP112021 300 AM MDT Tue Aug 10 2021 Deep convection associated with Kevin is still displaced well south and southwest of its exposed low-level center by strong northeasterly vertical wind shear. Recent scatterometer data indicate that the center is elongated from northeast to southwest, and the tropical-storm-force winds are confined to the southern semicircle of the cyclone. Based on several 35-kt wind vectors noted in the latest scatterometer passes, the initial intensity is held at 40 kt for this advisory. Satellite imagery indicates that Kevin has taken a northward jog overnight, and its estimated initial motion is now northwest or 305/8 kt. A general northwestward to west-northwestward motion is expected over the next several days as Kevin moves along the southwestern periphery of a deep-layer ridge. Based on the initial motion adjustment and guidance trends, the official NHC forecast track has been adjusted northward from the previous one, although it still lies a little to the south of the TVCE and HCCA aids. Moderate to strong northeasterly wind shear is forecast to persist over Kevin for the next day or so, which should limit its ability to strengthen despite favorable SSTs and abundant mid-level moisture. By the time that the wind shear diminishes, the cyclone will be passing over much cooler waters in a drier, more stable environment. Thus, little change in strength is expected in the near-term, followed by weakening beginning on Wednesday. Overall, the latest NHC intensity forecast remains near the multi-model consensus. By 72 h, GFS and ECMWF model simulated satellite imagery suggest that Kevin will be devoid of organized convection, and so the official NHC forecast shows Kevin as a remnant low at that time. FORECAST POSITIONS AND MAX WINDS INIT 10/0900Z 18.1N 113.3W 40 KT 45 MPH 12H 10/1800Z 18.8N 114.4W 40 KT 45 MPH 24H 11/0600Z 19.8N 115.6W 40 KT 45 MPH 36H 11/1800Z 21.0N 117.2W 35 KT 40 MPH 48H 12/0600Z 22.0N 119.4W 30 KT 35 MPH 60H 12/1800Z 22.9N 121.5W 25 KT 30 MPH 72H 13/0600Z 23.9N 123.6W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 14/0600Z 26.0N 128.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 15/0600Z 27.5N 131.5W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Reinhart/Pasch

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