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Tropical Storm ESTELLE Forecast Discussion Number 20

2016-07-20 10:39:37| National Hurricane Center (East Pacific)

Issued at 200 AM PDT WED JUL 20 2016 000 WTPZ41 KNHC 200839 TCDEP1 TROPICAL STORM ESTELLE DISCUSSION NUMBER 20 NWS NATIONAL HURRICANE CENTER MIAMI FL EP062016 200 AM PDT WED JUL 20 2016 Other than a brief warm spot appearing within the small CDO feature around 0400Z, the overall convective structure of Estelle has changed little since the previous advisory. Recent microwave satellite data, especially a 0531Z AMSU pass, continue to indicate that the cyclone has been unable to completely close off a mid-level eye feature. The initial intensity remains 60 kt based on an average of subjective and objective intensity estimates, and the lack of a persistent, well-developed eye feature in microwave data. Estelle has made a jog to the west, and the motion estimate is now 270/10 kt. Estelle is expected to continue on a westward track for the next 12 h or so, followed by a turn toward the west-northwest by this afternoon, a motion that is forecast to continue through 48 h. By 72 h and beyond, Estelle is expected to turn northwestward and move into a trough-induced break in the subtropical ridge around 130-135W longitude. The new NHC guidance is in good agreement on this scenario, and the official forecast track lies close to the previous advisory track and the consensus model TVCN. It isn't out of the question that Estelle could still briefly reach hurricane strength this morning. However, any strengthening that might occur will be short-lived now that the cyclone is moving over sub-26C sea-surface temperatures. Although the vertical wind shear is forecast by both the GFS and ECMWF models to remain quite low, sharply decreasing SSTs and much drier mid-level air should cause Estelle to steadily weaken after 12 h. The cyclone is forecast to become a post-tropical low in 48 h when Estelle will be moving over 22C SSTs, and dissipation is expected by 120 h. The new intensity forecast is essentially just an update of the previous advisory, and closely follows the intensity consensus model IVCN. FORECAST POSITIONS AND MAX WINDS INIT 20/0900Z 19.0N 122.0W 60 KT 70 MPH 12H 20/1800Z 19.4N 124.1W 60 KT 70 MPH 24H 21/0600Z 19.9N 126.7W 55 KT 65 MPH 36H 21/1800Z 20.6N 129.4W 45 KT 50 MPH 48H 22/0600Z 21.6N 132.0W 35 KT 40 MPH...POST-TROPICAL 72H 23/0600Z 24.5N 136.7W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 24/0600Z 28.1N 140.6W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 25/0600Z...DISSIPATED $$ Forecaster Stewart

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Tropical Storm DARBY Forecast Discussion Number 35

2016-07-20 10:38:01| National Hurricane Center (East Pacific)

Issued at 200 AM PDT WED JUL 20 2016 000 WTPZ45 KNHC 200837 TCDEP5 TROPICAL STORM DARBY DISCUSSION NUMBER 35 NWS NATIONAL HURRICANE CENTER MIAMI FL EP052016 200 AM PDT WED JUL 20 2016 Darby has changed little in structure during the past few hours. Deep convection with cloud tops as cold as -60C continue near the center, and recent microwave images showed a nearly closed mid-level ring. Dvorak Current Intensity numbers remain 3.5 from TAFB and SAB, and the initial intensity is therefore held at 55 kt. Darby is over SSTs around 25C and is heading toward warmer waters. However, vertical shear is expected to increase in the next 24-36 hours. Interestingly, the intensity models aren't in agreement on what will happen with Darby's intensity during this period. While the SHIPS and LGEM models indicate steady weakening over the next few days, the HWRF and Florida State Superensemble actually show some re-intensification in 24-36 hours. Due to these competing signals, the NHC official forecast shows little change in intensity during the next 48 hours, followed by gradual weakening on days 3-5. This updated forecast is not too different from the previous one, except that it delays steady weakening until after 48 hours. Darby is moving westward with an initial motion of 270/11 kt. The cyclone is located to the south of the subtropical ridge, which should maintain a westward motion for the next three days. After that time, a retrograding mid- to upper-level low north of the Hawaiian Islands will create a break in the ridge, causing Darby to turn northwestward and north-northwestward on days 4 and 5. With the exception of the GFDL, there is very little cross-track spread among the model guidance. However, there are some noticeable speed differences, with the ECMWF and UKMET showing more acceleration after the turn compared to the GFS and HWRF models. For now, the NHC official forecast, which is very similar to the previous forecast, splits the difference and is near a consensus of the GFS and ECMWF models. FORECAST POSITIONS AND MAX WINDS INIT 20/0900Z 20.0N 138.9W 55 KT 65 MPH 12H 20/1800Z 19.8N 140.6W 50 KT 60 MPH 24H 21/0600Z 19.5N 142.9W 50 KT 60 MPH 36H 21/1800Z 19.2N 145.2W 50 KT 60 MPH 48H 22/0600Z 18.9N 147.5W 50 KT 60 MPH 72H 23/0600Z 19.0N 151.0W 45 KT 50 MPH 96H 24/0600Z 20.0N 152.5W 45 KT 50 MPH 120H 25/0600Z 23.0N 154.0W 40 KT 45 MPH $$ Forecaster Berg

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Tropical Storm ESTELLE Forecast Discussion Number 19

2016-07-20 04:50:35| National Hurricane Center (East Pacific)

Issued at 800 PM PDT TUE JUL 19 2016 000 WTPZ41 KNHC 200250 TCDEP1 TROPICAL STORM ESTELLE DISCUSSION NUMBER 19 NWS NATIONAL HURRICANE CENTER MIAMI FL EP062016 800 PM PDT TUE JUL 19 2016 Convection near the center of Estelle has deepened and become more symmetric this evening. Microwave data show some improvement in inner-core structure as well, although the low- and mid-level centers are still somewhat separated. Subjective Dvorak classifications are a little higher than 6 hours ago, so the wind speed is raised to 60 kt. Little significant change in strength is forecast overnight since the cyclone is quickly approaching cooler waters. With the recent upward trends in organization, however, Estelle could sneak up to hurricane intensity during that time, and this is reflected in the official forecast. A gradual weakening should begin by late Wednesday since Estelle will be moving over much cooler waters, with remnant low status likely by late Friday. The new NHC prediction is similar to the previous one and the intensity consensus, adjusted slightly higher for the initial wind speed. In contrast to the tricky intensity forecasts for Estelle, the track forecasts have been straightforward. A persistent subtropical ridge should continue to steer the storm westward to west- northwestward for the next couple of days. The western portion of the ridge is finally forecast to erode in about 72 hours, which will likely cause Estelle or its remnants to turn northwestward by day 4. Guidance is in good agreement on this scenario, with a westward shift to the latest NHC track forecast to better reflect the newest model consensus. FORECAST POSITIONS AND MAX WINDS INIT 20/0300Z 19.1N 121.0W 60 KT 70 MPH 12H 20/1200Z 19.3N 122.8W 65 KT 75 MPH 24H 21/0000Z 19.7N 125.3W 60 KT 70 MPH 36H 21/1200Z 20.3N 127.8W 50 KT 60 MPH 48H 22/0000Z 21.1N 130.6W 40 KT 45 MPH 72H 23/0000Z 23.8N 135.5W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 24/0000Z 27.5N 139.5W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 25/0000Z...DISSIPATED $$ Forecaster Blake

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Tropical Storm DARBY Forecast Discussion Number 34

2016-07-20 04:32:01| National Hurricane Center (East Pacific)

Issued at 800 PM PDT TUE JUL 19 2016 000 WTPZ45 KNHC 200231 TCDEP5 TROPICAL STORM DARBY DISCUSSION NUMBER 34 NWS NATIONAL HURRICANE CENTER MIAMI FL EP052016 800 PM PDT TUE JUL 19 2016 Darby continues to maintain deep convection near its center, and in fact the convective cloud tops have cooled a bit over the past several hours. The current intensity estimate, 55 kt, is unchanged from the past advisory and is consistent with the latest Dvorak estimate from TAFB. The storm should encounter modestly increasing vertical shear and drier air over the next several days, but will be moving over slightly warmer waters. These factors should result in only a slow rate of weakening over the forecast period, and this is reflected in the official intensity forecast, which is near the model consensus and above the latest SHIPS and LGEM guidance. It is worth noting however, that longer-range intensity prediction has little skill. Based on geostationary and microwave fixes, the westward motion, 280/11 kt, continues. The track forecast reasoning has not changed. A mid-level subtropical ridge extending westward from the southern Great Plains should continue to steer Darby on a westward or slightly south-of-westward heading for the next few days. In the latter part of the forecast period, a mid-level cyclone to the north of the Hawaiian Islands should cause Darby to turn toward the northwest. The official forecast is very close to the multi-model consensus. However, the GFS and ECMWF ensemble tracks show considerable spread on days 3-5, indicating a significant amount of uncertainty in the forecast track late in the period. FORECAST POSITIONS AND MAX WINDS INIT 20/0300Z 20.0N 137.8W 55 KT 65 MPH 12H 20/1200Z 20.0N 139.5W 50 KT 60 MPH 24H 21/0000Z 19.8N 141.8W 50 KT 60 MPH 36H 21/1200Z 19.5N 144.1W 50 KT 60 MPH 48H 22/0000Z 19.2N 146.3W 45 KT 50 MPH 72H 23/0000Z 19.1N 150.2W 45 KT 50 MPH 96H 24/0000Z 20.2N 152.2W 45 KT 50 MPH 120H 25/0000Z 22.0N 154.0W 40 KT 45 MPH $$ Forecaster Pasch

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Tropical Storm ESTELLE Forecast Discussion Number 18

2016-07-19 22:36:27| National Hurricane Center (East Pacific)

Issued at 200 PM PDT TUE JUL 19 2016 000 WTPZ41 KNHC 192036 TCDEP1 TROPICAL STORM ESTELLE DISCUSSION NUMBER 18 NWS NATIONAL HURRICANE CENTER MIAMI FL EP062016 200 PM PDT TUE JUL 19 2016 Estelle has changed little in organization since this morning. The tropical storm still has several broken bands of convection around the circulation but microwave data indicate that there has been no improvement in the inner-core structure. Dvorak T-numbers from TAFB and SAB have decreased to T3.5, and the initial intensity is set to 55 kt for this advisory. Estelle's intensity forecasts have not been golden since the tropical cyclone has refused to strengthen during the past couple of days. There still appears to be a short window in which Estelle could strengthen, but given the lack of inner-core structure, it appears unlikely that significant intensification will occur. As a result, the NHC forecast now shows little change in wind speed tonight. Weakening should begin on Thursday and continue during the remainder of the period as Estelle moves over cooler water and into a more stable airmass. The tropical cyclone is expected to lose convection and become a remnant low within 72 hours. There has been no significant change to the track forecast or reasoning. Estelle continues moving west-northwestward to the south of the strong subtropical ridge that has steered all of the July eastern Pacific tropical cyclone westward to west- northwestward. The western portion of the ridge is finally forecast to weaken in about 72 hours, which should cause Estelle or its remnant low to turn northwestward by day 4. The track guidance is very tightly clustered and the NHC track is near an average of the GFS/ECMWF models. FORECAST POSITIONS AND MAX WINDS INIT 19/2100Z 19.0N 119.8W 55 KT 65 MPH 12H 20/0600Z 19.3N 121.5W 55 KT 65 MPH 24H 20/1800Z 19.7N 123.9W 50 KT 60 MPH 36H 21/0600Z 20.1N 126.4W 45 KT 50 MPH 48H 21/1800Z 21.1N 129.1W 35 KT 40 MPH 72H 22/1800Z 23.7N 134.1W 30 KT 35 MPH...POST-TROP/REMNT LOW 96H 23/1800Z 27.5N 138.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 120H 24/1800Z 31.0N 141.0W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Brown

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