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Tropical Depression Rene Forecast Discussion Number 9

2020-09-09 10:46:48| National Hurricane Center (Atlantic)

Issued at 500 AM AST Wed Sep 09 2020 000 WTNT43 KNHC 090846 TCDAT3 Tropical Depression Rene Discussion Number 9 NWS National Hurricane Center Miami FL AL182020 500 AM AST Wed Sep 09 2020 Satellite imagery indicates that convection associated with Rene is increasing and becoming better organized, with a broad convective band forming in the western semicircle. Satellite intensity estimates indicate that the cyclone is close to regaining tropical storm strength, but the initial intensity will be held at 30 kt to see if the convection persists and what upcoming scatterometer data shows. The initial motion is west-northwestward or 285/12 kt. There is little change in the forecast philosophy for the first 48-60 h of the forecast, with Rene expected to continue west-northwestward. This part of the new forecast track is similar to the previous track. After 60 h, much of the track guidance has shifted significantly to the left and shows less of a northward turn by 96-120 hr. This shift has left the GFS and the old forecast on the right side of the guidance envelope. This part of the new forecast track is moved to the left of the previous track, but it lies to the right of the various consensus models. If the current guidance trends continue, additional westward shifts of the later part of the forecast track may be necessary in subsequent advisories, Conditions appear generally favorable for Rene to strengthen during the next 48-60 h, although the cyclone will be moving over sea surface temperatures of near 26.5C during that time. The intensity forecast calls for Rene to re-intensify and become a hurricane by the 60 h point. After that, the cyclone is likely to encounter moderate to strong northwesterly shear which should cause weakening. The new intensity forecast is unchanged since the previous forecast, and it lies between the ICON and HCCA intensity consensus forecasts. FORECAST POSITIONS AND MAX WINDS INIT 09/0900Z 17.4N 30.5W 30 KT 35 MPH 12H 09/1800Z 17.9N 32.4W 35 KT 40 MPH 24H 10/0600Z 18.7N 34.6W 40 KT 45 MPH 36H 10/1800Z 19.6N 36.7W 50 KT 60 MPH 48H 11/0600Z 20.8N 38.7W 60 KT 70 MPH 60H 11/1800Z 22.2N 40.4W 65 KT 75 MPH 72H 12/0600Z 24.2N 41.9W 60 KT 70 MPH 96H 13/0600Z 28.0N 43.0W 50 KT 60 MPH 120H 14/0600Z 30.0N 42.5W 40 KT 45 MPH $$ Forecaster Beven

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Tropical Storm Paulette Forecast Discussion Number 10

2020-09-09 10:42:33| National Hurricane Center (Atlantic)

Issued at 500 AM AST Wed Sep 09 2020 000 WTNT42 KNHC 090842 TCDAT2 Tropical Storm Paulette Discussion Number 10 NWS National Hurricane Center Miami FL AL172020 500 AM AST Wed Sep 09 2020 The 20-30 kt of southwesterly shear continues to have a significant impact on Paulette's inner core. A 0615 UTC Global Precipitation Measurement (GPM) Microwave Imager overpass showed a severely sheared tropical cyclone with the exposed surface circulation displaced to the south of the cloud canopy. Although the objective ADT and an earlier SATCON analysis yield 45 kt, The initial intensity is held at a generous 50 kt for this advisory in deference to last night's scatterometer pass showing a few 50 kt winds. In addition to the moderate, persistent shear, the RAMMB/CIRA Average Vertical Instability parameter time series analysis revealed a higher than normal (1995-2010) statically stable environment, another potential inhibiting factor. This was further supported by the statistical-dynamical intensity models showing a rather parched mid-troposphere (less than 58%). Therefore, slow weakening of Paulette is forecast during the next few days. Toward the end of the period, the ECMWF and FV3 SHIPS intensity models continue to indicate a more southerly, diffluent pattern which should aid in some restrengthening, and this is indicated in the NHC forecast. The initial motion is estimated to be westward, or 280/7 kt. Paulette should turn west-northwestward later today and westward on Thursday around the southwestern periphery of a subtropical ridge to the northeast of the cyclone. A turn northwestward is predicted on Saturday as Paulette moves further into a growing weakness in the ridge over the western Atlantic. The official forecast is an update of the previous one through 72 hrs, then is shifted to the left through day 5 to lies between the HCCA consensus and the the HFIP/NUOPC Project's 5EMN 133 member multi-model ensemble mean. FORECAST POSITIONS AND MAX WINDS INIT 09/0900Z 19.2N 45.6W 50 KT 60 MPH 12H 09/1800Z 19.7N 46.9W 50 KT 60 MPH 24H 10/0600Z 20.3N 49.0W 45 KT 50 MPH 36H 10/1800Z 20.5N 50.7W 45 KT 50 MPH 48H 11/0600Z 20.8N 52.2W 40 KT 45 MPH 60H 11/1800Z 21.4N 53.6W 40 KT 45 MPH 72H 12/0600Z 22.7N 54.9W 40 KT 45 MPH 96H 13/0600Z 25.9N 58.2W 45 KT 50 MPH 120H 14/0600Z 28.7N 61.4W 50 KT 60 MPH $$ Forecaster Roberts

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Tropical Storm Paulette Forecast Discussion Number 9

2020-09-09 04:51:46| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Tue Sep 08 2020 000 WTNT42 KNHC 090251 TCDAT2 Tropical Storm Paulette Discussion Number 9 NWS National Hurricane Center Miami FL AL172020 1100 PM AST Tue Sep 08 2020 Microwave and satellite data suggest that vertical shear is weakening Paulette. The center is near the southern side of a large thunderstorm cluster, with the bulk of deep convection in the northeastern quadrant of the cyclone. A recent ASCAT-B pass showed maximum winds of 45-50 kt, a little lower than the other satellite estimates, and 50 kt is chosen as the initial wind speed. With Paulette already on a weakening trend, it seems that the window for significant strengthening has closed. More likely, a gradual decay of the storm is anticipated due to moderate or strong shear during the next few days. This shear could abate by the end of the forecast period due to Paulette moving around the northeastern side of a large mid-to-upper level low, which is a common position for the re-intensification of a tropical cyclone after encountering the mid-oceanic trough. The new forecast is lowered from the previous one for the first few days and then raised slightly at the longer ranges. This is consistent with a blend of the intensity model consensus, leaning toward the NOAA corrected-consensus guidance at the end. The storm is moving northwestward at about 8 kt. There has been some convergence of the model guidance during the next few days as Paulette should move west-northwestward tomorrow and westward on Thursday around a mid-level ridge. Thus, little change has been made from the previous forecast during the first 48-72h. Afterwards, the forecast is shifted to the north by 45-60 n mi under the assumption that Paulette stays coherent as a tropical cyclone and takes a turn to the northwest this weekend on the eastern flank of the aforementioned mid-to-upper level low. The new track forecast is northeast of the model consensus and places less emphasis on models, like the 12Z ECMWF, which show Paulette staying weaker and missing the full influence of the low. FORECAST POSITIONS AND MAX WINDS INIT 09/0300Z 19.2N 45.0W 50 KT 60 MPH 12H 09/1200Z 19.8N 46.2W 50 KT 60 MPH 24H 10/0000Z 20.2N 48.1W 50 KT 60 MPH 36H 10/1200Z 20.6N 50.0W 45 KT 50 MPH 48H 11/0000Z 20.8N 51.7W 45 KT 50 MPH 60H 11/1200Z 21.1N 52.9W 40 KT 45 MPH 72H 12/0000Z 21.9N 53.8W 40 KT 45 MPH 96H 13/0000Z 24.4N 55.7W 45 KT 50 MPH 120H 14/0000Z 27.5N 59.0W 55 KT 65 MPH $$ Forecaster Blake

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Tropical Depression Rene Forecast Discussion Number 8

2020-09-09 04:51:18| National Hurricane Center (Atlantic)

Issued at 200 AM CVT Wed Sep 09 2020 000 WTNT43 KNHC 090251 TCDAT3 Tropical Depression Rene Discussion Number 8 NWS National Hurricane Center Miami FL AL182020 200 AM CVT Wed Sep 09 2020 Rene's circulation remains fairly robust based on a 08/2148Z ASCAT-A overpass. However, the overall convective pattern has eroded significantly, and this is reflected in the ASCAT scatterometer wind data only showing surface winds of about 25 kt. Allowing for some undersampling, plus a recent increase in convection near the center, the intensity has only been lowered to 30 kt for this advisory. Rene remains beneath a pronounced upper-level anticyclone and outflow is fairly symmetrical in all quadrants. The initial motion is 285/14 kt. There continues to be no significant change to previous forecast track or reasoning. Rene is expected to move generally west-northwestward around the southwestern periphery of a deep-layer ridge for the next couple of days, followed by a decrease in forward speed and a turn toward the northwest on Friday and a motion toward the north on Saturday and Sunday. The latest NHC model guidance is in decent agreement on this developing steering flow pattern, thus the new NHC track forecast is essentially just an extension of the previous advisory track and lies close to a blend of the consensus models TVCA, GFEX, and NOAA-HCCA. Although Rene has weakened, a burst of strong convection with cloud tops colder than -80C has developed over and to the west of the center, while a fragmented band of convection has formed in the northern semicircle. These features strongly suggest that Rene is poised to restrengthen soon. Sea-surface temperatures are expected to be 26.0-26.5 deg C in the 24-60 h period, which are only marginal for strengthening to occur. However, mid-level humidity values are forecast to be near 70 percent and the cyclone is expected to remain under a favorable upper-level anticyclone during that time. Given these factors, slow but steady intensification is forecast, with Rene still expected to become a hurricane in 2-3 days. Thereafter, strong westerly to west-northwesterly vertical wind shear in excess of 25-30 kt is expected to cause Rene to weaken significantly on days 4 and 5. The new official intensity forecast is similar to but slightly lower than the previous intensity forecast, and is along the extreme upper portion of the guidance envelope and is above the intensity consensus models. FORECAST POSITIONS AND MAX WINDS INIT 09/0300Z 17.0N 29.3W 30 KT 35 MPH 12H 09/1200Z 17.5N 31.1W 35 KT 40 MPH 24H 10/0000Z 18.4N 33.7W 40 KT 45 MPH 36H 10/1200Z 19.3N 35.9W 50 KT 60 MPH 48H 11/0000Z 20.5N 38.1W 60 KT 70 MPH 60H 11/1200Z 22.1N 39.8W 65 KT 75 MPH 72H 12/0000Z 24.2N 41.4W 60 KT 70 MPH 96H 13/0000Z 28.5N 42.6W 50 KT 60 MPH 120H 14/0000Z 30.2N 40.3W 40 KT 45 MPH $$ Forecaster Stewart

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Tropical Storm Rene Forecast Discussion Number 7

2020-09-08 22:34:18| National Hurricane Center (Atlantic)

Issued at 800 PM CVT Tue Sep 08 2020 000 WTNT43 KNHC 082034 TCDAT3 Tropical Storm Rene Discussion Number 7 NWS National Hurricane Center Miami FL AL182020 800 PM CVT Tue Sep 08 2020 Rene has not changed much throughout the day. The storm is producing deep convection that is loosely organized in bands around the center. The satellite intensity estimates are unchanged from earlier and range from 25 kt to 40 kt. Based on these data and the earlier ASCAT pass, the initial intensity is again held at 35 kt. The eastern-most bands of Rene are now pulling west of the Cabo Verde Islands, and the Tropical Storm Warning for those islands has been discontinued. Although Rene has struggled to maintain its intensity during the past 24 hours, the models insist that the cyclone will begin to take advantage of the generally conducive conditions of low wind shear, high moisture, and relatively warm waters. Therefore, the NHC intensity forecast continues to show Rene strengthening to a hurricane in a couple of days. Beyond that time, however, Rene will likely be moving into an environment of strong westerly wind shear, which should cause the storm to weaken in the 3-5 day time period. This forecast is largely an update of the previous one and closely follows the IVCN model. The tropical storm continues to move westward at 14 kt. There has been no significant change to the track forecast reasoning. A mid-level ridge should continue to steer Rene westward to west-northwestward for the next couple of days. After that time, the storm should slow down and gradually turn to the north and then to the northeast as it moves into a weakness in the ridge. There is a little less spread in the guidance this cycle, but there remain differences in the models concerning where and how sharply Rene recurves. The NHC track forecast is similar to the previous one and lies close to the TVCA and TVCX consensus models. FORECAST POSITIONS AND MAX WINDS INIT 08/2100Z 16.8N 27.9W 35 KT 40 MPH 12H 09/0600Z 17.2N 29.6W 40 KT 45 MPH 24H 09/1800Z 18.0N 32.2W 50 KT 60 MPH 36H 10/0600Z 18.9N 34.8W 60 KT 70 MPH 48H 10/1800Z 19.9N 37.0W 65 KT 75 MPH 60H 11/0600Z 21.3N 38.8W 70 KT 80 MPH 72H 11/1800Z 23.2N 40.3W 65 KT 75 MPH 96H 12/1800Z 27.7N 42.2W 55 KT 65 MPH 120H 13/1800Z 30.5N 40.5W 50 KT 60 MPH $$ Forecaster Cangialosi

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