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Tropical Depression Rene Forecast Discussion Number 27

2020-09-13 22:42:00| National Hurricane Center (Atlantic)

Issued at 500 PM AST Sun Sep 13 2020 000 WTNT43 KNHC 132041 TCDAT3 Tropical Depression Rene Discussion Number 27 NWS National Hurricane Center Miami FL AL182020 500 PM AST Sun Sep 13 2020 Rene continues to produce occasional small bursts of deep convection, most recently to the north of its surface center. Both the TAFB and SAB Dvorak classifications indicated that convection at 18Z was insufficient to classify the system, an indication that the few pop up thunderstorms are not sufficiently organized to classify the system as a tropical cyclone. That said, convection has increased a little since that time and there is a possibility that deep convection could increase further this evening. While Rene is still a tropical depression for the moment, if its convection does not persist, it could become a remnant low as soon as tonight. Only very small changes were made to the NHC track and intensity forecasts. Rene's forward speed has continued to slow down since this morning. The shallow cyclone should make a westward and then southwestward turn during the next day or two, steered by a building low-level ridge to the north. Regardless of its exact status, Rene will probably continue to produce only a few small disorganized bursts of convection for the next few days while its circulation gradually spins down. Surrounding dry air and large-scale subsidence will likely prevent the redevelopment of more signifcant shower or thunderstorm activity. Most of the dynamical guidance indicates that Rene will open into a trough of low pressure within about 72 h, if not sooner and the NHC forecast shows likewise. FORECAST POSITIONS AND MAX WINDS INIT 13/2100Z 27.3N 47.6W 25 KT 30 MPH 12H 14/0600Z 27.7N 48.1W 25 KT 30 MPH 24H 14/1800Z 27.4N 48.7W 20 KT 25 MPH...POST-TROP/REMNT LOW 36H 15/0600Z 26.9N 49.6W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 15/1800Z 26.3N 50.7W 20 KT 25 MPH...POST-TROP/REMNT LOW 60H 16/0600Z 25.7N 52.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 16/1800Z...DISSIPATED $$ Forecaster Zelinsky

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Hurricane Paulette Forecast Discussion Number 28

2020-09-13 22:39:28| National Hurricane Center (Atlantic)

Issued at 500 PM AST Sun Sep 13 2020 000 WTNT42 KNHC 132039 TCDAT2 Hurricane Paulette Discussion Number 28 NWS National Hurricane Center Miami FL AL172020 500 PM AST Sun Sep 13 2020 Paulette has recovered from the dry air intrusion that was eroding the eastern eyewall this morning. A ring of deep convection with cloud tops ranging from about -50 to -65 C now completely surrounds a partially cleared eye. An Air Force Hurricane Hunter aircraft investigating the hurricane earlier this afternoon measured peak flight-level winds of 84 kt, which reduces to about 67 kt at the surface. However, since that time there has been steady improvement in the satellite presentation, and the latest Dvorak satellite T-numbers from TAFB and SAB are now at 4.5, supporting increasing the initial intensity to 75 kt for this advisory. Paulette is expected to remain in a low-shear environment over warm SSTs for the next 24-36 h, so gradual strengthening is likely during that time. Around 48 h from now, vertical wind shear is forecast to rapidly increase ahead of an approaching mid- upper level trough. This should cause the cyclone to begin weakening. By 72 h, Paulette is expected to be over waters less that 26 degrees C and should remain over cooler waters for the remainder of the forecast period. Around that same time, global models are indicating that the cyclone will begin to interact with a frontal boundary associated with the aforementioned trough. This should induce a gradual transition of Paulette to an extratropical cyclone, and that transition should be completed by 120 h, if not sooner. The latest NHC intensity forecast is little changed from the previous one and shows Paulette continuing to strengthen as it passes near or over Bermuda early Monday. The forecast also shows Paulette becoming a major hurricane by Monday night, after the cyclone has moved away from Bermuda. This intensity forecast is in good agreement with the HFIP corrected consensus, HCCA. Paulette is moving northwestward at 11 kt, to the southwest of a mid-level ridge. There is no change to the forecast track reasoning. This northwest motion should continue until just after the cyclone passes Bermuda Monday morning. Later on Monday, the hurricane should turn north, then northeastward, as it rounds the periphery of the ridge. After turning northeastward, the cyclone is expected to accelerate as it gets picked up in the mid-latitude flow ahead of the approaching trough. Later on in the forecast period a slower eastward motion is indicated once the trough bypasses the cyclone. The latest NHC forecast was nudged only slightly to the left of the previous one, and is in agreement with tightly clustered global and regional track guidance. Tropical storm conditions should reach Bermuda in the next couple of hours, with hurricane force winds arriving there overnight. Key Messages: 1. Paulette is expected to approach Bermuda as a hurricane today and will be near the island tonight and Monday. A prolonged period of strong winds, storm surge, and heavy rainfall is expected on Bermuda beginning this 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 13/2100Z 30.6N 63.1W 75 KT 85 MPH 12H 14/0600Z 31.8N 64.5W 85 KT 100 MPH 24H 14/1800Z 33.9N 64.8W 95 KT 110 MPH 36H 15/0600Z 36.1N 62.4W 100 KT 115 MPH 48H 15/1800Z 38.1N 57.8W 100 KT 115 MPH 60H 16/0600Z 40.3N 52.6W 95 KT 110 MPH 72H 16/1800Z 42.4N 47.4W 80 KT 90 MPH 96H 17/1800Z 45.5N 38.7W 60 KT 70 MPH 120H 18/1800Z 44.4N 34.1W 45 KT 50 MPH...POST-TROP/EXTRATROP $$ Forecaster Latto

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Tropical Storm Karina Forecast Discussion Number 4

2020-09-13 22:36:17| National Hurricane Center (East Pacific)

Issued at 200 PM PDT Sun Sep 13 2020 000 WTPZ41 KNHC 132036 TCDEP1 Tropical Storm Karina Discussion Number 4 NWS National Hurricane Center Miami FL EP162020 200 PM PDT Sun Sep 13 2020 A midday ASCAT pass revealed that Karina still has an elongated circulation and is likely still attached to the ITCZ/monsoon trough. The center is also displaced to the northeast of the deepest convection due to ongoing moderate northeasterly shear. The ASCAT data confirmed that the storm currently has maximum winds of 40 k, with most of the tropical-storm-force winds located over the southern semicircle. With the shear not expected to decrease from its current magnitude, only modest strengthening is expected during the next 36 hours or so while Karina remains over waters warmer than 26 degrees Celsius. The peak intensity shown in the official forecast has been adjusted downward to 50 kt, which is now the highest intensity shown by any of the intensity models. Colder waters and a drier, more stable atmosphere should induce gradual weakening after day 2, with Karina likely to lose all of its deep convection and become a remnant low by day 4. Karina turned a little bit to the left today but still has a west-northwestward heading (290/10 kt). A mid-level ridge located to the north should keep Karina on a west-northwestward trajectory with some reduction in forward speed through day 4. Once it weakens to a remnant low, Karina is expected to turn westward, steered by lower-level trade winds. There is some north-south divergence among the track models during Karina's expected remnant low stage, but the overall guidance envelope has not shifted. Therefore, the updated NHC track forecast is not too different from the previous one and lies close to the HCCA, Florida State Superensemble, and TVCE multi-model consensus. FORECAST POSITIONS AND MAX WINDS INIT 13/2100Z 17.8N 116.0W 40 KT 45 MPH 12H 14/0600Z 18.5N 117.1W 45 KT 50 MPH 24H 14/1800Z 19.1N 118.6W 45 KT 50 MPH 36H 15/0600Z 19.8N 120.1W 50 KT 60 MPH 48H 15/1800Z 20.5N 121.3W 45 KT 50 MPH 60H 16/0600Z 21.2N 122.4W 40 KT 45 MPH 72H 16/1800Z 21.9N 123.6W 35 KT 40 MPH 96H 17/1800Z 22.5N 126.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 120H 18/1800Z 22.5N 128.5W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Berg

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Tropical Depression Twenty Forecast Discussion Number 5

2020-09-13 22:34:19| National Hurricane Center (Atlantic)

Issued at 500 PM AST Sun Sep 13 2020 000 WTNT45 KNHC 132034 TCDAT5 Tropical Depression Twenty Discussion Number 5 NWS National Hurricane Center Miami FL AL202020 500 PM AST Sun Sep 13 2020 The depression's center is a little closer to the deep convection compared to this morning, but the overall structure has not changed significantly. Based on this morning's ASCAT pass, and recent Dvorak estimates of T2.0 from TAFB and SAB, the initial intensity remains 30 kt. The northerly shear over the system has been analyzed to have decreased since this morning (now around 10 kt), which is probably why the center is closer to the convection. The shear is forecast to decrease further, and once the depression becomes more detached from the ITCZ/monsoon trough, it is expected to go through a significant phase of strengthening as it heads west toward higher oceanic heat content and a more unstable atmosphere. As discussed this morning, the GFS-based SHIPS guidance indicates that there is a 50-50 chance that the depression will strengthen by at least 65 kt during the next 3 days, which is 10 times higher than the climatological mean. And, all three regional hurricane models (HWRF, HMON, and COAMPS-TC), as well as the HCCA aid, show the cyclone becoming a major hurricane by the end of the forecast period. As a result, the NHC intensity forecast has been adjusted upward and now explicitly shows major hurricane strength on days 4 and 5. The motion remains west-northwestward (290/10 kt), with the depression located south of a large mid-level high centered over the central Atlantic. This feature should continue driving the system westward or west-northwestward for the next 2 days. After that time, the ridge is expected to shift northward, causing the potentially strengthening hurricane to move a little slower toward the northwest. Most of the track models are clustered close together, although the HWRF remains a southern outlier and the ECMWF model is a little slower and on the right side of the envelope. The new NHC track forecast has not moved much from the previous prediction and now lies closest to the HFIP Corrected Consensus. FORECAST POSITIONS AND MAX WINDS INIT 13/2100Z 12.7N 37.6W 30 KT 35 MPH 12H 14/0600Z 13.2N 39.5W 35 KT 40 MPH 24H 14/1800Z 13.6N 42.1W 45 KT 50 MPH 36H 15/0600Z 14.1N 44.4W 60 KT 70 MPH 48H 15/1800Z 14.7N 46.3W 70 KT 80 MPH 60H 16/0600Z 15.6N 47.7W 80 KT 90 MPH 72H 16/1800Z 16.8N 49.0W 90 KT 105 MPH 96H 17/1800Z 19.5N 51.5W 100 KT 115 MPH 120H 18/1800Z 22.5N 54.0W 100 KT 115 MPH $$ Forecaster Berg

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Tropical Depression Rene Forecast Discussion Number 26

2020-09-13 17:02:36| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Sun Sep 13 2020 000 WTNT43 KNHC 131502 TCDAT3 Tropical Depression Rene Discussion Number 26 NWS National Hurricane Center Miami FL AL182020 1100 AM AST Sun Sep 13 2020 Sporadic small areas of convection continue to fire off around the circulation of Rene, only to dissipate shortly thereafter. A recent ASCAT overpass showed an area of 20 to 25 kt winds in the eastern semicircle. Therefore, the initial intensity will remain 25 kt. The dry environment surrounding Rene will only get drier over the next couple of days. That, along with increasing subsidence over the cyclone should eventually cause Rene to become a remnant low. There is no change to the previous forecast intensity or timing of the system becoming a remnant low, which is consistent with the global models. Rene is beginning to slow down as a ridge starts to build to the north and northwest of the cyclone. This slowing trend should continue through tonight. Late Monday through Tuesday, a turn to the west then southwest should occur as whatever remains of the system becomes steered by the larger circulation of Tropical Depression Twenty to its southwest. There is little change to the previous track forecast, and the latest NHC forecast lies near the various multi-model track consensus guidance. FORECAST POSITIONS AND MAX WINDS INIT 13/1500Z 26.8N 47.6W 25 KT 30 MPH 12H 14/0000Z 27.5N 48.3W 25 KT 30 MPH 24H 14/1200Z 27.6N 48.8W 25 KT 30 MPH 36H 15/0000Z 27.3N 49.6W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 15/1200Z 26.7N 50.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 60H 16/0000Z 26.1N 51.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 16/1200Z...DISSIPATED $$ Forecaster Latto

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