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Tropical Storm Karina Forecast Discussion Number 2

2020-09-13 11:02:00| National Hurricane Center (East Pacific)

Issued at 300 AM MDT Sun Sep 13 2020 ZCZC MIATCDEP1 ALL TTAA00 KNHC DDHHMM Tropical Storm Karina Discussion Number 2 NWS National Hurricane Center Miami FL EP162020 300 AM MDT Sun Sep 13 2020 Recent scatterometer data showed an area of 30-35 kt winds within about 80 n mi of the center of Tropical Depression Sixteen-E in the southwestern quadrant. Based on this data, along with 35-40 kt intensity estimates from TAFB and the CIMSS satellite consensus, the depression is upgraded to Tropical Storm Karina with an initial intensity of 35 kt. Satellite imagery show that the system is still being affected by northeasterly vertical shear, with the low-level center exposed to the northeast of the main convective mass. The initial motion is now 310/10. The global models forecast a mid-level ridge to build westward to the north of Karina in a day or two, causing the cyclone to move west- northwestward. A more westward motion is expected near the end of the forecast period as a weakening Karin is steered more by the low-level trade winds. The track guidance is in fair agreement with this scenario, although there is some spread in the forward speed, possibly due differences in how Karina interacts with the larger ITCZ/monsoon trough circulation, including the remnants of Invest 91E. The new forecast track will follow the forward speed of the consensus models and has only minor adjustments from the previous track. The forecast track takes the center of Karin over cooler water, with the system crossing the 25-26C isotherms in 48-72 h. Present indications are that the shear will decrease a little before the 72 h point, so the intensity forecast calls for gradual strengthening during that time. After 72 h, the cooler water and dry air entrainment should cause weakening. The new intensity forecast has some minor adjustments from the previous forecast, and it is in best agreement with the HCCA corrected consensus model and the Florida State Superensemble. FORECAST POSITIONS AND MAX WINDS INIT 13/0900Z 17.4N 113.8W 35 KT 40 MPH 12H 13/1800Z 18.1N 114.8W 40 KT 45 MPH 24H 14/0600Z 18.8N 116.4W 45 KT 50 MPH 36H 14/1800Z 19.4N 118.0W 50 KT 60 MPH 48H 15/0600Z 19.9N 119.4W 55 KT 65 MPH 60H 15/1800Z 20.5N 120.7W 55 KT 65 MPH 72H 16/0600Z 21.2N 122.0W 55 KT 65 MPH 96H 17/0600Z 22.0N 124.5W 45 KT 50 MPH 120H 18/0600Z 22.0N 127.0W 30 KT 35 MPH $$ Forecaster Beven NNNN

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Tropical Depression Rene Forecast Discussion Number 25

2020-09-13 10:59:01| National Hurricane Center (Atlantic)

Issued at 500 AM AST Sun Sep 13 2020 404 WTNT43 KNHC 130858 TCDAT3 Tropical Depression Rene Discussion Number 25 NWS National Hurricane Center Miami FL AL182020 500 AM AST Sun Sep 13 2020 Rene is producing a round of disorganized convection at this time, with the convection now displaced to the east of the center by increasing west-northwesterly vertical shear. The initial intensity remains 25 kt based on a combination of satellite intensity estimates and continuity from the previous advisory. The strong shear and a dry environment should lead to Rene degenerating to a remnant low pressure area between 24-36 h, with the global models in good agreement that the remnant low should weaken to a trough by 72 h. The new intensity forecast is unchanged from the previous forecast. The initial motion is 325/12. A blocking ridge of high pressure is forecast to build to the northwest or Rene during the next day or two, causing the cyclone to slow down and then turn westward. After that time, a west-southwestward motion is expected as Rene or its remnants are steered by a combination of the ridge and the circulation of Tropical Depression 20 to the southeast. There is little change to either the track guidance or the forecast track from the previous advisory. FORECAST POSITIONS AND MAX WINDS INIT 13/0900Z 26.2N 47.1W 25 KT 30 MPH 12H 13/1800Z 27.2N 47.9W 25 KT 30 MPH 24H 14/0600Z 27.7N 48.5W 25 KT 30 MPH 36H 14/1800Z 27.6N 49.1W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 15/0600Z 27.2N 50.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 60H 15/1800Z 26.7N 51.1W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 16/0600Z...DISSIPATED $$ Forecaster Beven

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Tropical Depression Twenty Forecast Discussion Number 3

2020-09-13 10:54:07| National Hurricane Center (Atlantic)

Issued at 500 AM AST Sun Sep 13 2020 000 WTNT45 KNHC 130853 TCDAT5 Tropical Depression Twenty Discussion Number 3 NWS National Hurricane Center Miami FL AL202020 500 AM AST Sun Sep 13 2020 The depression remains poorly organized and elongated from northeast-to-southwest. Convection mainly consists of small curved but fragmented bands in the southern semicircle. Satellite intensity estimates remain unchanged as a result, so the initial intensity will also remain unchanged at 30 kt. The initial motion estimate is 295/09 kt. The ridge to the north and east of the tropical depression is forecast to remain intact for the next 5 days, keeping the cyclone on a general west-northwestward track through 72 hours, followed by a northwestward motion toward the weakness in the ridge on days 4 and 5. The latest NHC guidance remains in very good agreement on this developing track scenario and, thus, no significant changes were made to the previous advisory track. Due to the negative influence of the long low-level westerly fetch associated with the monsoon trough that the cyclone is embedded within, it will likely another 24 hours or so for the low-level wind field to become better organized. However, once that occurs, environmental conditions are expected to be favorable for steady strengthening on days 2-4, followed by gradual weakening on ay 5 due to increasing southwesterly vertical wind shear. The new NHC intensity forecast is similar to the previous advisory forecast, and lies near the upper end of the intensity guidance envelope. FORECAST POSITIONS AND MAX WINDS INIT 13/0900Z 12.2N 35.5W 30 KT 35 MPH 12H 13/1800Z 12.6N 36.9W 30 KT 35 MPH 24H 14/0600Z 13.2N 39.2W 40 KT 45 MPH 36H 14/1800Z 13.7N 41.5W 50 KT 60 MPH 48H 15/0600Z 14.4N 43.8W 60 KT 70 MPH 60H 15/1800Z 15.3N 45.7W 70 KT 80 MPH 72H 16/0600Z 16.3N 46.9W 80 KT 90 MPH 96H 17/0600Z 19.0N 49.6W 90 KT 105 MPH 120H 18/0600Z 21.5N 51.8W 85 KT 100 MPH $$ Forecaster Stewart

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Hurricane Paulette Forecast Discussion Number 26

2020-09-13 10:51:35| National Hurricane Center (Atlantic)

Issued at 500 AM AST Sun Sep 13 2020 000 WTNT42 KNHC 130851 TCDAT2 Hurricane Paulette Discussion Number 26 NWS National Hurricane Center Miami FL AL172020 500 AM AST Sun Sep 13 2020 Over the past 6 hours, conventional and passive microwave satellite data indicate that very little change to Paulette's overall convective cloud pattern and inner-core structure has occurred. A recent GMI pass indciated that the inner-core convection remains somewhat disheveled due to a narrow but pronounced band of dry air having penetrated the mid-levels of the cyclone. However, the low-level eye feature remains intact with a diameter of at least 30 nmi. Given the little change in structure since the previous reconnaissance mission, the intensity is being maintained at 65 kt. Another Air Force Reserve Hurricane Hunter aircraft will be investigating Paulette later this morning to provide a better estimate of the hurricane's intensity. The initial motion estimate remains west-northwestward or 300/12 kt. Overall, there is no significant change to the previous track forecast or reasoning. The global and regional models are in excellent agreement on Paulette passing over or near Bermuda during the 24-36 hour period as the cyclone rounds a sharp east-to-west oriented subtropical ridge located near and due east of Bermuda. After passing Bermuda and moving north of the ridge in about 36 hours, Paulette is forecast to accelerate northeastward ahead of an approaching deep-layer trough and associated surface cold front. There is one important feature to mention -- the official forecast track is west of the latest 0600 UTC interpolated models due to the interpolated model tracks taking the center of Paulette at least 30 nmi east of Bermuda. In contrast, the GFS, UKMET, and ECMWF are less than 6 nmi apart at 12-48 hours, and that consensus brings the hurricane across or just west of Bermuda in about 30 hours. Therefore, the new NHC official track forecast is essentially just an update and extension of the previous advisory track, and lies just west of the tightly packed NHC guidance envelope. Environmental conditions appear favorable to Paulette to strengthen during the next 72 hours or so, with only occasional intrusions of dry mid-level air briefly interrupting the intensification process. The ragged inner core structure will likely delay intensification this morning, but by the this afternoon and continuing into Monday, the vertical shear is forecast by the global models to decrease to near zero, which should allow for significant strengthening to occur. In fact, it highly probable that Paulette will continue to intensify as the hurricane passes over Bermuda. By 48 hours when the hurricane is expected to be north of Bermuda, baroclinic interaction with the aforementioned deep-layer trough is forecast to aid in the intensification process with Paulette possibly becoming a major hurricane around 72 hours. Thereafter, increasing vertical wind shear in excess of 25 kt should gradually weaken the cyclone. It is possible that by 96 hours or so, Paulette could merge with a frontal system and become a powerful extratropical low. For now, however, Paulette is forecast to remain just ahead of the front within the warm sector of a flat frontal wave. The official intensity forecast is similar to the previous advisory, and is near the upper end of intensity guidance throughout the 120-h forecast period. Key Messages: 1. Paulette is expected to approach Bermuda as a hurricane on Sunday and will be near the island Sunday night and Monday. A prolonged period of strong winds, storm surge, and heavy rainfall is expected on Bermuda beginning Sunday evening, and a hurricane warning is in effect for the island. Preparations to protect life and property should be rushed to completion. 2. Swells produced by Paulette are affecting portions of the Leeward Islands, the Greater Antilles, the Bahamas, Bermuda, and the east coast of the United States. These swells could cause life-threatening surf and rip current conditions. FORECAST POSITIONS AND MAX WINDS INIT 13/0900Z 29.4N 60.8W 65 KT 75 MPH 12H 13/1800Z 30.2N 62.5W 70 KT 80 MPH 24H 14/0600Z 31.8N 64.4W 80 KT 90 MPH 36H 14/1800Z 34.0N 65.0W 90 KT 105 MPH 48H 15/0600Z 35.9N 62.4W 95 KT 110 MPH 60H 15/1800Z 37.8N 57.9W 95 KT 110 MPH 72H 16/0600Z 39.3N 54.0W 90 KT 105 MPH 96H 17/0600Z 42.0N 46.0W 80 KT 90 MPH 120H 18/0600Z 43.8N 40.0W 65 KT 75 MPH $$ Forecaster Stewart

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Tropical Depression Twenty Forecast Discussion Number 2

2020-09-13 04:47:27| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Sat Sep 12 2020 000 WTNT45 KNHC 130247 TCDAT5 Tropical Depression Twenty Discussion Number 2 NWS National Hurricane Center Miami FL AL202020 1100 PM AST Sat Sep 12 2020 The depression is poorly organized at this time. A large convective band wraps around the northern and western portions of the cyclone, but its center of circulation is exposed and appears to have become somewhat elongated. Recent ASCAT data and the latest TAFB Dvorak analysis indicate that the maximum winds remain near 30 kt. It will take some time for the depression to get better organized, and only slight strengthening is anticipated during the next 24 h. After that time, the cyclone's environment is expected to support intensification, and the intensity guidance is quite aggressive. While the exact timing is somewhat uncertain, it is probable that the system will become a hurricane early next week. The new NHC intensity forecast has been adjusted higher than the previous advisory beyond 48 h, but it is below or near the model consensus at all times. Little change was made to the NHC track forecast. The depression appears to be moving generally west-northwestward near 9 kt. In general, the system should continue west-northwestward for the next couple of days, with some slight fluctuations in its track possible tonight and tomorrow as the center consolidates. A weakness in the subtropical ridge is expected to develop by the middle of next week that could steer the cyclone more toward the northwest. The guidance is in very good agreement on this general scenario, though confidence in the forecast will be somewhat low until the system becomes a little better organized and strengthens. The official forecast is based primarily on the HCCA and TVCA consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 13/0300Z 11.9N 34.6W 30 KT 35 MPH 12H 13/1200Z 12.3N 35.9W 30 KT 35 MPH 24H 14/0000Z 12.9N 37.7W 35 KT 40 MPH 36H 14/1200Z 13.5N 40.1W 45 KT 50 MPH 48H 15/0000Z 14.1N 42.5W 55 KT 65 MPH 60H 15/1200Z 14.8N 44.5W 65 KT 75 MPH 72H 16/0000Z 15.9N 46.2W 80 KT 90 MPH 96H 17/0000Z 18.5N 49.0W 90 KT 105 MPH 120H 18/0000Z 21.5N 51.0W 90 KT 105 MPH $$ Forecaster Zelinsky

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