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Tropical Depression Nine-E Forecast Discussion Number 9
2021-08-05 04:40:15| National Hurricane Center (East Pacific)
Issued at 500 PM HST Wed Aug 04 2021 000 WTPZ44 KNHC 050240 TCDEP4 Tropical Depression Nine-E Discussion Number 9 NWS National Hurricane Center Miami FL EP092021 500 PM HST Wed Aug 04 2021 The system has not become noticeably better organized since earlier today, with a small area of deep convection near the center and some slightly curved bands of convection well removed to the east and northeast of the center. Microwave imagery also suggests little change in structure. The current intensity is held at 30 kt for now, in agreement with earlier scatterometer observations. Although the center fixes have some scatter, my best estimate for motion is slowly northwestward, or 325/6 kt. A mid-level ridge to the northeast of the tropical cyclone is forecast to be maintained for the next 48-72 hours. This should keep the system on a generally northwestward heading until late in the forecast period. By that time, the weakening cyclone should turn a little to the left following the low-level environmental winds. The official track forecast is similar to the previous one and just to the right of the multi-model consensus, in slight deference to the GFS solution which is even farther to the right of these tracks. Since the system should be in a fairly moist, low-shear environment for the next day or so, at least some slight strengthening seems likely. Thereafter, cooler SSTs and increased shear should cause weakening. The official intensity forecast is near or above most of the model guidance. FORECAST POSITIONS AND MAX WINDS INIT 05/0300Z 15.3N 136.2W 30 KT 35 MPH 12H 05/1200Z 16.0N 136.6W 35 KT 40 MPH 24H 06/0000Z 16.9N 137.7W 40 KT 45 MPH 36H 06/1200Z 17.8N 138.9W 35 KT 40 MPH 48H 07/0000Z 18.8N 140.3W 30 KT 35 MPH 60H 07/1200Z 19.8N 142.0W 30 KT 35 MPH 72H 08/0000Z 20.5N 143.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 09/0000Z 22.0N 147.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 10/0000Z...DISSIPATED $$ Forecaster Pasch
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Tropical Storm Hilda Forecast Discussion Number 22
2021-08-05 04:35:50| National Hurricane Center (East Pacific)
Issued at 800 PM PDT Wed Aug 04 2021 000 WTPZ43 KNHC 050235 TCDEP3 Tropical Storm Hilda Discussion Number 22 NWS National Hurricane Center Miami FL EP082021 800 PM PDT Wed Aug 04 2021 Hilda's satellite appearance has changed little over the past several hours. Small bursts of moderate to deep convection persist in the eastern semicircle of the system, and the low-level center is still partially exposed to the west of the convective cloud mass. Without any recent scatterometer data, the initial intensity is held at 35 kt for this advisory, in best agreement with a T2.5/35 kt Dvorak classification from TAFB. A subtropical ridge over the eastern North Pacific continues to steer Hilda west-northwestward, or 290/7 kt. This general motion is expected to continue for the next day or so, followed by a slight westward turn on Friday as the shallow cyclone becomes steered by a low-level ridge to its north. While most of the models show limited interaction between Hilda and TD Nine-E to its southwest, it is worth noting that the GFS moves both Nine-E and Hilda much farther northward than the rest of the guidance. The GFS solution is not favored at this time, and the latest NHC track forecast remains very similar to the previous one and lies near the multi-model guidance consensus. Hilda is not expected to remain a tropical storm for much longer. As sea surface temperatures decrease along its track and the cyclone moves into a drier, more stable environment, it will become increasingly difficult for Hilda to sustain organized convection near its center. The latest NHC forecast calls for Hilda to weaken to a tropical depression on Thursday and degenerate to a 25-kt remnant low on Friday morning. Then, the global models agree that the system should open into a trough and dissipate by Saturday morning well east of the Hawaiian Islands. FORECAST POSITIONS AND MAX WINDS INIT 05/0300Z 19.6N 128.7W 35 KT 40 MPH 12H 05/1200Z 20.2N 130.2W 30 KT 35 MPH 24H 06/0000Z 21.3N 132.4W 30 KT 35 MPH 36H 06/1200Z 22.1N 134.6W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 07/0000Z 22.6N 137.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 60H 07/1200Z...DISSIPATED $$ Forecaster Reinhart/Pasch
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Tropical Depression Nine-E Forecast Discussion Number 8
2021-08-04 22:35:46| National Hurricane Center (East Pacific)
Issued at 1100 AM HST Wed Aug 04 2021 000 WTPZ44 KNHC 042035 TCDEP4 Tropical Depression Nine-E Discussion Number 8 NWS National Hurricane Center Miami FL EP092021 1100 AM HST Wed Aug 04 2021 Satellite images today indicate that the system has been maintaining two hooking bands of convection to the north and south of the center. In addition, scatterometer data shows a well-defined, albeit a touch elongated, center and 30-kt winds. Thus, advisories are being re-started on Tropical Depression Nine-E after a 3-day hiatus, with an initial intensity of 30 kt. The depression probably only has a few days as a tropical cyclone again because SSTs begin to drop off in a day or so, along with increasing shear and mid-level dry air. Nine-E does have a chance to finally become a tropical storm in the meantime before the aforementioned environmental conditions get less conducive on Friday. The system is likely to degenerate into a remnant low again this weekend (or sooner) as it encounters a very hostile environment. The NHC wind speed forecast is close to the model consensus, but is a smidge higher near peak intensity, owing to the HCCA corrected-consensus guidance. The depression has been moving slowly toward the north-northwest today. A distant mid-level ridge to the northeast is providing the steering for the cyclone. This ridge should strengthen somewhat during the next few days, causing the depression to gradually turn to the northwest on Thursday and continue that motion through late week. Similar to a lot of forecasts this year, the GFS-based guidance is on the right side of the track envelope while the ECMWF and UKMET solutions lie on the left side. The official track assumes that the GFS shows a bit too deep of a tropical cyclone, and so the NHC prediction leans just west of the consensus throughout the forecast period. FORECAST POSITIONS AND MAX WINDS INIT 04/2100Z 14.9N 135.7W 30 KT 35 MPH 12H 05/0600Z 15.6N 136.1W 35 KT 40 MPH 24H 05/1800Z 16.5N 136.8W 40 KT 45 MPH 36H 06/0600Z 17.4N 138.0W 35 KT 40 MPH 48H 06/1800Z 18.4N 139.4W 30 KT 35 MPH 60H 07/0600Z 19.5N 141.0W 30 KT 35 MPH 72H 07/1800Z 20.5N 142.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 08/1800Z 21.5N 146.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 09/1800Z...DISSIPATED $$ Forecaster Blake
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Tropical Storm Hilda Forecast Discussion Number 21
2021-08-04 22:34:47| National Hurricane Center (East Pacific)
Issued at 200 PM PDT Wed Aug 04 2021 000 WTPZ43 KNHC 042034 TCDEP3 Tropical Storm Hilda Discussion Number 21 NWS National Hurricane Center Miami FL EP082021 200 PM PDT Wed Aug 04 2021 Convection associated with Hilda continues to weaken and shrink in areal coverage due to modest northwesterly vertical wind shear, sub-25C sea-surface temperatures (SSTs), and entrainment of stable, cold-air stratocumulus clouds. A 1656Z partial ASCAT-A scatterometer pass revealed two 33-kt vectors in the southeastern quadrant in the radius-of-maximum winds. Even allowing for some undersampling, this indicates that Hilda is barely hanging on to tropical storm status, and the initial intensity will remain at 35 kt for this advisory. Model analyses show virtually no instability in the center of and north of Hilda right now, and with the cyclone forecast to move over even cooler water and into increasing westerly wind shear during the next 12-24 hours, a rapid decrease in both the convection and cyclone's intensity appears to be forthcoming soon. Hilda is forecast to become a depression later tonight and a remnant low on Thursday. Dissipation is expected by late Friday or Saturday well to the east of the Hawaiian Islands. The latest NHC official intensity forecast is similar to the previous advisory, and follows a blend of the HCCA and IVCN consensus intensity models. Hilda continues on a steady west-northwestward course or 295/08 kt. This general motion is expected to continue into Thursday, followed by a more westward motion on Friday and Saturday as a low- to mid-level ridge builds to north of Hilda on days 2 and 3. The official NHC track forecast is essentially just an update of the previous advisory track, and lies along the southern edge of the guidance envelope between the tightly packed consensus track models to the north and the ECMWF model to the south. FORECAST POSITIONS AND MAX WINDS INIT 04/2100Z 19.4N 128.0W 35 KT 40 MPH 12H 05/0600Z 20.0N 129.4W 30 KT 35 MPH 24H 05/1800Z 21.0N 131.4W 25 KT 30 MPH 36H 06/0600Z 21.8N 133.7W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 06/1800Z 22.4N 136.1W 20 KT 25 MPH...POST-TROP/REMNT LOW 60H 07/0600Z 23.0N 138.4W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 07/1800Z...DISSIPATED $$ Forecaster Stewart
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Tropical Storm Hilda Forecast Discussion Number 20
2021-08-04 16:34:12| National Hurricane Center (East Pacific)
Issued at 800 AM PDT Wed Aug 04 2021 000 WTPZ43 KNHC 041434 TCDEP3 Tropical Storm Hilda Discussion Number 20 NWS National Hurricane Center Miami FL EP082021 800 AM PDT Wed Aug 04 2021 Hilda continues to weaken early this morning due to cool sea-surface temperatures (SST) and modest northerly vertical wind shear. The current intensity is estimated to be 35 kt based on an average of subjective satellite classifications of T2.5/35 kt from both TAFB and SAB, and objective estimates of 31 kt and 41 kt from UW-CIMSS ADT and SATCON, respectively. Hilda is currently moving over sub-25C SSTs with even cooler water and increasing westerly wind shear still ahead of the cyclone. As a result of these unfavorable environmental parameters, Hilda is forecast to weaken further, becoming a depression later today and a remnant low by late tonight or early Thursday. Dissipation is expected by late Friday or Saturday well to the east of the Hawaiian Islands. The new NHC official intensity forecast is similar to the previous advisory, and follows a blend of the HCCA and IVCN consensus intensity models. Hilda has been moving west-northwestward or 295/08 kt. This general motion should continue into Thursday. Low- to mid-level ridging to the north of Hilda is expected to gradually build westward over the next several days, forcing the cyclone and its remnants more westward on Friday and Saturday. The new NHC forecast track is essentially just an update of the previous advisory, and lies down the middle of the tightly packed consensus track models. FORECAST POSITIONS AND MAX WINDS INIT 04/1500Z 19.1N 127.4W 35 KT 40 MPH 12H 05/0000Z 19.7N 128.7W 30 KT 35 MPH 24H 05/1200Z 20.6N 130.6W 25 KT 30 MPH 36H 06/0000Z 21.5N 132.6W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 06/1200Z 22.2N 135.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 60H 07/0000Z 22.7N 137.3W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 07/1200Z...DISSIPATED $$ Forecaster Stewart
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