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Tropical Depression Hilda Forecast Discussion Number 25
2021-08-05 22:31:35| National Hurricane Center (East Pacific)
Issued at 200 PM PDT Thu Aug 05 2021 000 WTPZ43 KNHC 052031 TCDEP3 Tropical Depression Hilda Discussion Number 25 NWS National Hurricane Center Miami FL EP082021 200 PM PDT Thu Aug 05 2021 Stubborn Hilda refuses to go away. Convection has been pulsing since the previous advisory with cloud tops fluctuating between -30C and -60C in the northeastern quadrant. However, this convection hasn't mixed higher winds downward into the boundary based on a 1634Z ASCAT-A scatterometer pass, which showed 30-31-kt wind vectors north of the center and outside of the convection. The initial intensity is being maintained at 30 kt for this advisory based on the aforementioned ASCAT surface wind data. Gradual weakening should occur now that Hilda is firmly located over sub-23 deg C sea-surface temperatures and will be moving into a drier and more stable air mass. Visible satellite imagery already shows an extensive field of cold-air stratocumulus clouds being entrained into much of the low-level circulation. Hilda is forecast to degenerate into a remnant low tonight or early Friday, and open up into a trough by the weekend, well east of the Hawaiian Islands. The initial motion estimate is 300/11 kt. Hilda should continue on a west-northwestward trajectory for the next couple of days, being steered by a deep-layer subtropical ridge to the north. The latest NHC track forecast is essentially just an update of the previous advisory track, and lies down the middle of the tightly packed consensus models. FORECAST POSITIONS AND MAX WINDS INIT 05/2100Z 21.5N 131.2W 30 KT 35 MPH 12H 06/0600Z 22.2N 132.8W 25 KT 30 MPH 24H 06/1800Z 23.0N 135.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 07/0600Z 23.7N 137.2W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 07/1800Z 24.4N 139.3W 15 KT 15 MPH...POST-TROP/REMNT LOW 60H 08/0600Z...DISSIPATED $$ Forecaster Stewart
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Tropical Storm Jimena Forecast Discussion Number 11
2021-08-05 16:37:31| National Hurricane Center (East Pacific)
Issued at 500 AM HST Thu Aug 05 2021 000 WTPZ44 KNHC 051437 TCDEP4 Tropical Storm Jimena Discussion Number 11 NWS National Hurricane Center Miami FL EP092021 500 AM HST Thu Aug 05 2021 Conventional satellite imagery indicates that Jimena's cloud pattern has changed little during the past several hours, although most recently, enhanced infrared images show some warming of the cloud tops just west of the center. Timely AMSR-2 and GMI passive microwave color composite images revealed a well-developed banding feature wrapping around the surface center from the north and west portions of the cyclone. The initial intensity is held at 35 kt and is in agreement with the Dvorak satellite intensity estimates from TAFB and SAB. The large-scale models and the statistical-dynamical SHIPS intensity guidance (GFS/ECMWF) show that the previously noted period of conducive atmospheric and oceanic conditions should be ending soon. By the 36-hour period, sub-25C sea-surface temperatures and a gradually stabilizing/drier surrounding air mass should cause Jimena to weaken. Guidance also shows increasing west-northwesterly shear beyond 48 hours. Accordingly, the NHC forecast calls for Jimena to weaken to a depression by mid-period, and degenerate into a remnant low in 60 hours. Based on the aforementioned microwave images, the initial motion is estimated to be northwestward, or 315/6 kt. A subtropical ridge anchored to the northeast of the cyclone is forecast to steer Jimena toward the northwest through the 48 period. Afterward, a turn toward the west-northwest is expected as the vertically shallow system is influenced more by the easterly tradewinds. The official forecast is basically an update of the previous one and lies near the multi-model consensus (TVCN) aid. FORECAST POSITIONS AND MAX WINDS INIT 05/1500Z 16.1N 137.2W 35 KT 40 MPH 12H 06/0000Z 16.5N 137.7W 35 KT 40 MPH 24H 06/1200Z 17.5N 138.9W 35 KT 40 MPH 36H 07/0000Z 18.5N 140.2W 30 KT 35 MPH 48H 07/1200Z 19.5N 141.5W 30 KT 35 MPH 60H 08/0000Z 20.3N 142.9W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 08/1200Z 20.9N 144.3W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 09/1200Z...DISSIPATED $$ Forecaster Roberts
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Tropical Depression Hilda Forecast Discussion Number 24
2021-08-05 16:34:31| National Hurricane Center (East Pacific)
Issued at 800 AM PDT Thu Aug 05 2021 000 WTPZ43 KNHC 051434 TCDEP3 Tropical Depression Hilda Discussion Number 24 NWS National Hurricane Center Miami FL EP082021 800 AM PDT Thu Aug 05 2021 After an earlier brief burst of thunderstorm activity northeast of the center around 0600Z, associated convection since then has been on a rapid decline and warming of the cloud tops which now barely reach -30 deg C near the center. The initial intensity has been lowered to 30 kt based on a blend of Dvorak T- and CI-numbers of T2.5 and T1.5 from both TAFB and SAB, and an objective satellite intensity estimate of 2.0/30 kt from UW-CIMSS ADT, making Hilda a tropical depression. Further weakening is expected now that Hilda is located over sub-23 deg C sea-surface temperatures and moving into a drier and more stable air mass. The cyclone is forecast to degenerate into a remnant low later today and open up into a trough by the weekend, well east of the Hawaiian Islands. The initial motion estimate is 305/11 kt, which is faster and a little to the right of the previous advisory motion. This is likely due to the low- and upper-level circulations having decoupled now, owing to the lack of significant convection. The weakening cyclone should be steered west-northwestward for the next 48 hours by a sprawling subtropical ridge located to the north. The new NHC forecast track is similar to the previous advisory track and lies down the middle of the tightly packed consensus models. FORECAST POSITIONS AND MAX WINDS INIT 05/1500Z 21.0N 130.2W 30 KT 35 MPH 12H 06/0000Z 21.7N 131.8W 25 KT 30 MPH 24H 06/1200Z 22.5N 133.9W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 07/0000Z 23.2N 136.1W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 07/1200Z 23.9N 138.3W 15 KT 15 MPH...POST-TROP/REMNT LOW 60H 08/0000Z...DISSIPATED $$ Forecaster Stewart
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Tropical Storm Hilda Forecast Discussion Number 23
2021-08-05 10:41:36| National Hurricane Center (East Pacific)
Issued at 200 AM PDT Thu Aug 05 2021 000 WTPZ43 KNHC 050841 TCDEP3 Tropical Storm Hilda Discussion Number 23 NWS National Hurricane Center Miami FL EP082021 200 AM PDT Thu Aug 05 2021 Hilda is maintaining a small, but shrinking area of deep convection, which has rotated from the southeast to northern portion of the storm's circulation. A 0405 UTC ASCAT-A and 0522 UTC ASCAT-B pass had peak wind retrievals of 36 and 40 kt respectively, about 40 n mi northeast of Hilda's center. This scatterometer data suggests that the storm might have been stronger than estimated yesterday when the convection was more robust. However, given the warming cloud tops and shrinking area of convection since that time, the initial advisory intensity was kept at 35 kt, which still agrees with the most recent subjective Dvorak estimate from TAFB. Hilda is moving to the west-northwest at 8 kt as the tropical cyclone remains steered by a large subtropical ridge over the eastern North Pacific. As the storm becomes more shallow, its general motion should bend westward and gradually accelerate due to the influence of a large low-level ridge centered well northward. The latest track guidance is slightly more poleward early on, and the NHC track forecast was nudged a bit further north, but remains a bit south of the HFIP corrected consensus approach (HCCA). As noted previously, the GFS model forecast remains a northern outlier, with more interaction between Hilda and recently upgraded Jimena, and its solution is not favored at this time. As Hilda continues to move over increasingly cool ocean waters and into a drier and more stable environment, the remaining deep convection will likely dissipate at some point later today. Additional convective bursts thereafter will become increasingly unlikely. The latest NHC forecast expects Hilda to weaken to a tropical depression later today and become a remnant low by tomorrow. This solution is favored by most of the intensity guidance. The remnant low is then forecast to open up into a trough by the weekend, well east of the Hawaiian Islands. FORECAST POSITIONS AND MAX WINDS INIT 05/0900Z 20.1N 129.2W 35 KT 40 MPH 12H 05/1800Z 20.9N 130.7W 30 KT 35 MPH 24H 06/0600Z 21.9N 132.9W 30 KT 35 MPH 36H 06/1800Z 22.6N 135.1W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 07/0600Z 23.2N 137.3W 20 KT 25 MPH...POST-TROP/REMNT LOW 60H 07/1800Z...DISSIPATED $$ Forecaster Papin/Beven
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Tropical Storm Jimena Forecast Discussion Number 10
2021-08-05 10:35:54| National Hurricane Center (East Pacific)
Issued at 1100 PM HST Wed Aug 04 2021 000 WTPZ44 KNHC 050835 TCDEP4 Tropical Storm Jimena Discussion Number 10 NWS National Hurricane Center Miami FL EP092021 1100 PM HST Wed Aug 04 2021 Deep convection has increased near the center of the cyclone during the last several hours, and an outer convective band is present in the southeastern semicircle. Subjective satellite intensity estimates are 35 kt from TAFB and SAB, and the CIMSS satellite consensus estimate is 39 kt. Based on these data, the system is upgraded to Tropical Storm Jimena with 35-kt winds. The initial motion is 315/6 kt. A mid-level ridge to the northeast of the tropical cyclone is forecast to continue for the next 2-3 days, and this should keep Jimena moving generally northwestward. After that time, a west-northwestward motion is expected as the weakening system is steered more by the low-level flow. The track guidance models have shifted a bit to the right since the previous advisory. Therefore, the official forecast will also be nudged to the right. However, the new forecast track still lies to the left of the consensus models. While Jimena is in a moist and low-shear environment, the storm is moving over decreasing sea surface temperatures, with the center forecast to be over 25 C water in about 24 h. Thus, little additional strengthening is expected. After 24 h, the system should weaken due to even colder SSTs and increasing shear. The new intensity forecast has only minor tweaks from the previous forecast, and it lies near the upper edge of the intensity guidance. FORECAST POSITIONS AND MAX WINDS INIT 05/0900Z 15.5N 136.6W 35 KT 40 MPH 12H 05/1800Z 16.2N 137.2W 35 KT 40 MPH 24H 06/0600Z 17.1N 138.4W 35 KT 40 MPH 36H 06/1800Z 18.0N 139.5W 35 KT 40 MPH 48H 07/0600Z 19.0N 140.9W 30 KT 35 MPH 60H 07/1800Z 20.0N 142.4W 30 KT 35 MPH 72H 08/0600Z 21.0N 143.9W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 09/0600Z 22.0N 147.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 10/0600Z...DISSIPATED $$ Forecaster Beven
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