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Tropical Depression Hernan Forecast Discussion Number 10
2020-08-28 16:42:45| National Hurricane Center (East Pacific)
Issued at 900 AM MDT Fri Aug 28 2020 000 WTPZ43 KNHC 281442 TCDEP3 Tropical Depression Hernan Discussion Number 10 NWS National Hurricane Center Miami FL EP132020 900 AM MDT Fri Aug 28 2020 Satellite imagery shows that Hernan has become less organized since the last advisory with most of the associated convection dissipating. In addition, surface observations in the coastal areas near the cyclone suggest the possibility that it no longer has a closed circulation, although there are no observations over water to confirm this. Based on decreasing satellite intensity estimates, Hernan is downgraded to a tropical depression. Additional weakening is forecast, and Hernan is expected to degenerate to a remnant low pressure area as it moves over the Baja California peninsula later today and tonight. The system is then expected to weaken to a trough on Saturday. The initial motion is a somewhat uncertain 295/18. Hernan is moving around the northeastern side of the monsoon gyre that contains Tropical Storm Iselle, and a general west-northwestward motion is expected until the system dissipates on Saturday. FORECAST POSITIONS AND MAX WINDS INIT 28/1500Z 23.4N 109.1W 30 KT 35 MPH 12H 29/0000Z 24.1N 110.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 24H 29/1200Z...DISSIPATED $$ Forecaster Beven
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Tropical Storm Iselle Forecast Discussion Number 8
2020-08-28 10:32:02| National Hurricane Center (East Pacific)
Issued at 200 AM PDT Fri Aug 28 2020 000 WTPZ44 KNHC 280831 TCDEP4 Tropical Storm Iselle Discussion Number 8 NWS National Hurricane Center Miami FL EP142020 200 AM PDT Fri Aug 28 2020 Iselle continues to produce deep convection near the center and on its west side. This asymmetric cloud pattern is due to a moderate amount of easterly wind shear. An ASCAT-A overpass from a few hours ago showed maximum winds in the 45-50 kt range, and based on that data, the initial intensity is nudged up to 50 kt. The intensity models suggest that little change in strength is likely today as Iselle remains in the current environment of easterly shear. However, gradual weakening should begin by tonight and continue through the weekend as Iselle moves over progressively cooler waters and into a more stable air mass. The NHC intensity forecast follows the trend of the models, and predicts Iselle to weaken to a tropical depression in a couple of days and to a remnant low shortly thereafter. Iselle is moving slowly northeastward toward Tropical Storm Hernan located near the coast of west-central Mexico. Iselle should generally move northeastward to north-northeastward as it remains embedded in a trough with Hernan for about another day. Thereafter, Hernan is expected to dissipate and a low- to mid-level ridge should cause Iselle to turn to the northwest. This track keeps Iselle well offshore the Baja California peninsula. The models are in fair agreement, and this forecast lies close to the various consensus aids. The initial wind radii have been modified based on the aforementioned ASCAT data. FORECAST POSITIONS AND MAX WINDS INIT 28/0900Z 17.9N 115.0W 50 KT 60 MPH 12H 28/1800Z 18.7N 114.5W 50 KT 60 MPH 24H 29/0600Z 20.1N 114.1W 45 KT 50 MPH 36H 29/1800Z 21.7N 114.1W 40 KT 45 MPH 48H 30/0600Z 23.0N 114.8W 30 KT 35 MPH 60H 30/1800Z 23.9N 115.6W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 31/0600Z 24.2N 116.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 01/0600Z 24.5N 117.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 02/0600Z...DISSIPATED $$ Forecaster Cangialosi
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Tropical Storm Hernan Forecast Discussion Number 9
2020-08-28 10:09:25| National Hurricane Center (East Pacific)
Issued at 300 AM MDT Fri Aug 28 2020 000 WTPZ43 KNHC 280809 TCDEP3 Tropical Storm Hernan Discussion Number 9 NWS National Hurricane Center Miami FL EP132020 300 AM MDT Fri Aug 28 2020 Shortly after the release of the previous advisory, microwave imagery from a WindSat overpass showed no indication of a well-defined center near Hernan's estimated location. However,there was a hint of a small vortex well to the northeast. Subsequent ASCAT data showed that the well-defined vortex had moved near the Islas Marias and had winds of 30-35 kt. Data from the Geostationary Lightning Mapper showed a continuous maximum in lightning near Hernan's center from yesterday afternoon through the new estimated position. Confidence is therefore fairly high that Hernan has persisted as a tropical cyclone, at least through 0400 UTC this morning. Due to the northeastward relocation of the center, the track forecast has been significantly changed in that direction and now shows Hernan entering the Gulf of California later today. Hernan appears to be quickly moving around a larger low-level cyclonic gyre centered just west of the coast of Mexico. The gyre could steer Hernan or its remnants over the Baja California peninsula later today or early Saturday, but it is not forecast to have sustained tropical-storm-force winds at that time. All of the global models show Hernan opening into a trough within about 24 hours, but it could happen much sooner than that- possibly before Hernan even reaches the Gulf of California. If Hernan does make it to the coast as a depression or remnant low, it could produce some gusty winds before it quickly weakens and dissipates. FORECAST POSITIONS AND MAX WINDS INIT 28/0900Z 22.7N 107.3W 35 KT 40 MPH 12H 28/1800Z 23.6N 108.9W 35 KT 40 MPH 24H 29/0600Z 24.2N 110.6W 30 KT 35 MPH...POST-TROPICAL 36H 29/1800Z...DISSIPATED $$ Forecaster Zelinsky
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Tropical Storm Iselle Forecast Discussion Number 7
2020-08-28 04:36:27| National Hurricane Center (East Pacific)
Issued at 800 PM PDT Thu Aug 27 2020 000 WTPZ44 KNHC 280236 TCDEP4 Tropical Storm Iselle Discussion Number 7 NWS National Hurricane Center Miami FL EP142020 800 PM PDT Thu Aug 27 2020 Iselle continues to produce bursts of deep convection in an environment of moderate easterly shear, with the latest round of convection completely covering the low-level center. Since satellite classifications haven't changed much since the previous advisory, the initial intensity is left at 45 kt based on the earlier ASCAT data. There is some uncertainty in exactly how strong the shear currently is, with SHIPS diagnostics showing nearly 30 kt while UW-CIMSS is analyzing a little under 20 kt. A recent SSMIS pass showed some defined curved banding, so I'm inclined to think the shear is closer to the lower estimate. With that said, the SHIPS diagnostics do show the shear relaxing just a bit during the next 12-24 hours, which could allow Iselle to strengthen a little, and this scenario is supported by the latest HWRF, HMON, COAMPS-TC, HCCA, and GFS model solutions. After that time, the shear is expected to strengthen again, and then Iselle will be moving over cooler waters. Therefore, the new NHC intensity forecast is very close to the previous one from 24 hours and beyond. Iselle is likely to lose all of its convection and become a remnant low in about 3 days and then open up into a trough by day 5. Iselle is embedded in an elongated mid-level trough which extends northeastward to Tropical Storm Hernan near the coast of Mexico, and its initial motion is north-northeastward, or 030/3 kt. The interaction between the two tropical storms is expected to cause Iselle to continue moving north-northeastward or northward during the first 2 days. Once Hernan dissipates and Iselle weakens, a low-level ridge over northern Mexico should cause Iselle to turn toward the northwest and west on days 3 and 4. The track models have shifted a bit to the northeast after 48 hours, leaving the previous forecast near the left side of the guidance envelope, so the new NHC forecast was adjusted closer to the multi-model consensus aids during that period. FORECAST POSITIONS AND MAX WINDS INIT 28/0300Z 17.6N 115.5W 45 KT 50 MPH 12H 28/1200Z 18.2N 115.0W 50 KT 60 MPH 24H 29/0000Z 19.1N 114.5W 45 KT 50 MPH 36H 29/1200Z 20.1N 114.2W 40 KT 45 MPH 48H 30/0000Z 21.7N 114.2W 35 KT 40 MPH 60H 30/1200Z 23.2N 114.7W 30 KT 35 MPH 72H 31/0000Z 23.9N 115.7W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 01/0000Z 23.9N 117.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 120H 02/0000Z...DISSIPATED $$ Forecaster Berg
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Tropical Depression Laura Forecast Discussion Number 33
2020-08-28 04:34:55| National Hurricane Center (Atlantic)
Issued at 1000 PM CDT Thu Aug 27 2020 000 WTNT43 KNHC 280234 TCDAT3 Tropical Depression Laura Discussion Number 33 NWS National Hurricane Center Miami FL AL132020 1000 PM CDT Thu Aug 27 2020 Laura has continued to spin down after being over land for nearly a day. Surface observations no longer support tropical storm intensity, and therefore the system is being downgraded to a tropical depression. The cyclone should become a post-tropical low within a couple of days, and then transform into an extratropical cyclone while moving off the U.S. east coast. The official forecast shows some restrengthening in 2-4 days due to baroclinic processes. However, by the end of the forecast period, the system should be absorbed by a larger extratropical cyclone to the east of the Canadian Maritimes. Laura continues to move north-northeastward or at about 015/13 kt. A turn toward the northeast and east-northeast with increasing forward speed is likely while the cyclone becomes embedded in the stronger westerly flow. The official track forecast follows the latest dynamical model consensus. There is a continued threat of flooding from Laura for the next couple of days. This is the last NHC advisory on Laura. Future information on this system, including the rainfall threat, can be found in Public Advisories issued by the Weather Prediction Center beginning at 4 AM CDT, under AWIPS header TCPAT3, WMO header WTNT33 KWNH, and on the web at http://www.wpc.ncep.noaa.gov Key Messages: 1. Additional rainfall will continue to lead to flash flooding along small streams, urban areas, roadways, and minor to moderate river flooding across portions of Louisiana, Mississippi and Arkansas. The heavy rainfall threat and flash and urban flooding potential will spread northeastward into the middle-Mississippi, lower Ohio and Tennessee Valleys, and Mid-Atlantic States Friday and Saturday. 2. A few tornadoes remain possible this evening across eastern Arkansas, western Tennessee, northern Mississippi, and the Missouri Bootheel. The risk for a few tornadoes is expected to redevelop Friday afternoon into the evening across parts of the Mid-South and Tennessee Valley regions. FORECAST POSITIONS AND MAX WINDS INIT 28/0300Z 35.1N 92.0W 30 KT 35 MPH...INLAND 12H 28/1200Z 36.3N 91.0W 30 KT 35 MPH...INLAND 24H 29/0000Z 37.3N 87.8W 25 KT 30 MPH...INLAND 36H 29/1200Z 38.0N 82.3W 25 KT 30 MPH...POST-TROP/INLAND 48H 30/0000Z 38.5N 75.5W 25 KT 30 MPH...POST-TROP/EXTRATROP 60H 30/1200Z 41.5N 67.5W 35 KT 40 MPH...POST-TROP/EXTRATROP 72H 31/0000Z 44.0N 60.5W 45 KT 50 MPH...POST-TROP/EXTRATROP 96H 01/0000Z 48.0N 52.0W 40 KT 45 MPH...POST-TROP/EXTRATROP 120H 02/0000Z...DISSIPATED $$ Forecaster Pasch
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