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Tropical Storm Franklin Forecast Discussion Number 5

2017-08-07 22:34:02| National Hurricane Center (Atlantic)

Issued at 400 PM CDT Mon Aug 07 2017 000 WTNT42 KNHC 072033 TCDAT2 Tropical Storm Franklin Discussion Number 5 NWS National Hurricane Center Miami FL AL072017 400 PM CDT Mon Aug 07 2017 Visible satellite imagery continues to show a fairly well-organized tropical cyclone, although infrared images indicate some warming of the convective cloud tops. Observations from an Air Force Hurricane Hunter aircraft show that the storm has a fairly broad inner core, which is consistent with the ragged eye-like feature noted on the visible imagery. The current intensity is kept at 50 kt based on a blend of SFMR and flight-level observations from the aircraft along with sampling considerations. Franklin has a well-defined, symmetric upper-level outflow pattern, and some strengthening is still expected prior to landfall. Although the cyclone could be near hurricane strength at landfall on the east coast of the Yucatan peninsula, the broad inner core of the system would argue against rapid intensification during the next 12 hours. Weakening will occur due to the passage over the Yucatan peninsula, and restrengthening over the very warm waters of the Bay of Campeche is forecast. Although northerly shear could inhibit strengthening somewhat, Franklin is predicted to become a hurricane before making landfall in mainland Mexico. The official intensity forecast is similar to the latest HFIP Corrected Consensus forecast. Based on center fixes from the aircraft along with geostationary and microwave imagery, the initial motion is northwestward or 310/11 kt. The track forecast reasoning remains basically unchanged. A mid-level high pressure area near the northwestern Gulf of Mexico coast should force Franklin to take a west-northwestward to westward course for the next several days. FORECAST POSITIONS AND MAX WINDS INIT 07/2100Z 18.6N 85.9W 50 KT 60 MPH 12H 08/0600Z 19.1N 87.6W 60 KT 70 MPH...INLAND 24H 08/1800Z 19.9N 89.9W 40 KT 45 MPH...INLAND 36H 09/0600Z 20.3N 91.9W 50 KT 60 MPH...OVER WATER 48H 09/1800Z 20.5N 94.0W 65 KT 75 MPH...OVER WATER 72H 10/1800Z 20.5N 98.5W 55 KT 65 MPH...INLAND 96H 11/1800Z...DISSIPATED $$ Forecaster Pasch

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Tropical Storm Franklin Forecast Discussion Number 4

2017-08-07 16:34:31| National Hurricane Center (Atlantic)

Issued at 1000 AM CDT Mon Aug 07 2017 000 WTNT42 KNHC 071434 TCDAT2 Tropical Storm Franklin Discussion Number 4 NWS National Hurricane Center Miami FL AL072017 1000 AM CDT Mon Aug 07 2017 Visible and microwave satellite imagery shows that Franklin's cloud pattern is becoming better organized with banding features starting to appear. Inner-core convection is not very abundant over the southwest quadrant and the center is still estimated to be located near the southwest edge of the main cloud mass. Given the increase in organization after the 12Z Dvorak intensity estimate of 45 kt from TAFB, the advisory intensity is set to 50 kt. An Air Force Hurricane Hunter aircraft is scheduled to investigate Franklin this afternoon and should provide a better estimate of the strength of the storm. The upper-level environment is becoming increasingly conducive for intensification, with anticyclonic outflow becoming established over the tropical cyclone during the next couple of days. Franklin could become a hurricane before its first landfall, but interaction with the Yucatan Peninsula will cause some weakening on Tuesday. Thereafter, Franklin will be moving over SSTs near 30 deg C, which of course favors strengthening. A complicating factor at days 2 and 3 could be some northerly shear associated with an upper-level ridge over northeastern Mexico, as indicated by the global models. Nonetheless Franklin should be near or at hurricane intensity by the time it makes landfall in mainland Mexico. The official intensity forecast is a little above the model consensus. The initial motion continues to be west-northwestward or 300/12 kt. Little changes have been made to the track forecast from previous advisories. The steering environment remains fairly simple, and is dominated by a zonally-oriented ridge that should cause a west-northwestward to westward motion for the next several days. The official track forecast is close to the dynamical model consensus TVCN and leans slightly toward the ECMWF at the end of the period. FORECAST POSITIONS AND MAX WINDS INIT 07/1500Z 17.7N 85.1W 50 KT 60 MPH 12H 08/0000Z 18.5N 86.8W 60 KT 70 MPH 24H 08/1200Z 19.5N 88.9W 40 KT 45 MPH...INLAND 36H 09/0000Z 20.1N 91.1W 45 KT 50 MPH...OVER WATER 48H 09/1200Z 20.5N 93.3W 60 KT 70 MPH...OVER WATER 72H 10/1200Z 20.8N 97.8W 60 KT 70 MPH...INLAND 96H 11/1200Z...DISSIPATED $$ Forecaster Pasch

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Tropical Storm Franklin Forecast Discussion Number 3

2017-08-07 10:49:32| National Hurricane Center (Atlantic)

Issued at 500 AM EDT Mon Aug 07 2017 000 WTNT42 KNHC 070849 TCDAT2 Tropical Storm Franklin Discussion Number 3 NWS National Hurricane Center Miami FL AL072017 500 AM EDT Mon Aug 07 2017 Deep convection associated with Franklin has been steadily increasing in both coverage and vertical depth since the previous advisory. Wind data from a late-arriving 0231Z ASCAT-A pass suggest that Franklin might not have had a closed surface circulation at that time. However, the new GOES-16 nighttime microphysics imagery clearly shows low clouds moving from west to east on the south side of the alleged center, which is suggestive of a closed low-level circulation. The intensity has been nudged upward to 40 kt based on sustained winds of 39 kt measured at 4-meters elevation from NOAA buoy 42057 located about 110 nmi east of the center. The initial motion estimate is 300/12 kt. The latest NHC model guidance remains in excellent agreement that Franklin will continue to move west-northwestward along the south side of a deep-layer ridge during the next 48 hours or so, making landfall along the east coast of the Yucatan peninsula in 18-24 hours. After the cyclone crosses over Yucatan and moves into the Bay of Campeche by Wednesday, a more westward motion is expected thereafter as the ridge currently situated over northern Mexico and the southwestern U.S. builds southward. The track model guidance is tightly clustered around the previous forecast track, so the new forecast track is just an extension of the previous one and lies down the middle of the guidance envelope. Upper-level outflow continues to expand in the western semicircle, and a pronounced poleward outflow channel has developed in the northern semicircle, which is being aided by a large upper-level low located north of Puerto Rico. Although UW-CIMSS wind analyses indicate that modest westerly mid-level shear is still affecting the cyclone, that hindrance is forecast to abate in another 6 h or so. Both the GFS and ECMWF models are forecasting the deep-layer and mid-level shear to decrease to near zero in the 12-24 h period, suggesting that Franklin could undergo a period of rapid intensification right up until landfall occurs. Unfortunately, the official intensity forecast does not directly reflect that possible intensification trend due to the 24-h position being inland over Yucatan with weakening occuring at that time due to land interaction. Franklin is likely to reach a peak intensity of about 60 kt or so prior to landfall, and for that reason the government of Mexico has issued a Hurricane Watch. The cyclone will weaken some as it moves over the Yucatan, but re-strengthening is expected after Franklin emerges over the very warm waters of the Bay of Campeche in the 48-72 h period. The NHC intensity forecast remains close to the higher SHIPS guidance at 24 hours, and is near the IVCN and HCCA consensus models after that time. FORECAST POSITIONS AND MAX WINDS INIT 07/0900Z 17.1N 84.2W 40 KT 45 MPH 12H 07/1800Z 18.0N 85.8W 50 KT 60 MPH 24H 08/0600Z 19.0N 88.0W 55 KT 65 MPH...INLAND 36H 08/1800Z 19.9N 90.2W 40 KT 45 MPH...INLAND 48H 09/0600Z 20.4N 92.3W 45 KT 50 MPH...OVER WATER 72H 10/0600Z 21.0N 96.4W 55 KT 65 MPH 96H 11/0600Z 21.1N 100.5W 25 KT 30 MPH...INLAND 120H 12/0600Z...DISSIPATED $$ Forecaster Stewart

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Tropical Storm Franklin Forecast Discussion Number 2

2017-08-07 04:45:28| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT Sun Aug 06 2017 000 WTNT42 KNHC 070245 TCDAT2 Tropical Storm Franklin Discussion Number 2 NWS National Hurricane Center Miami FL AL072017 1100 PM EDT Sun Aug 06 2017 Last-light visible satellite pictures from GOES-13 and GOES-16 indicated that the low-level circulation of the disturbance had become better defined and was located near the southwestern edge of the main convective mass. NOAA Buoy 42057, located about 90 n mi northeast of the center, has reported peak 1-minute winds around 35 kt during the past few hours and a gust to 43 kt. Because the system has developed a closed circulation and well-defined center, it is now classified as a tropical storm. Franklin becomes the sixth tropical storm of the 2017 Atlantic hurricane season. The upper-level outflow is beginning to expand over the western portion of the circulation, indicating that the shear over the system is decreasing. The global models are predicting that Franklin will remain in a low-shear environment during the next several days, and the only limiting factor for intensification appears to be land interaction. Additional strengthening is expected before the cyclone reaches the Yucatan peninsula in about 24 hours. After the system moves over the Bay of Campeche, warm waters and favorable upper-level winds should allow for restrengthening, and although not explicitly indicated in the official forecast, Franklin could become a hurricane before it makes final landfall in mainland Mexico. The NHC forecast is closest to the higher SHIPS guidance at 24 hours, and is near the intensity consensus and HCCA models after that time. The initial motion estimate is 295/11. Franklin is forecast to move west-northwestward during the next several days to the south of a mid-level ridge that should remain in place over the northern Gulf of Mexico. The track model guidance has trended slightly southward after 48 hours, and the new NHC track forecast has been adjusted in that direction. The NHC forecast remains near the consensus of the GFS and ECMWF models. FORECAST POSITIONS AND MAX WINDS INIT 07/0300Z 16.4N 83.0W 35 KT 40 MPH 12H 07/1200Z 17.4N 84.9W 40 KT 45 MPH 24H 08/0000Z 18.5N 87.1W 50 KT 60 MPH 36H 08/1200Z 19.5N 89.3W 35 KT 40 MPH...INLAND 48H 09/0000Z 20.2N 91.3W 40 KT 45 MPH...OVER WATER 72H 10/0000Z 20.9N 95.2W 60 KT 70 MPH 96H 11/0000Z 21.0N 99.5W 35 KT 40 MPH...INLAND 120H 12/0000Z...DISSIPATED $$ Forecaster Brown

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Potential Tropical Cyclone Seven Forecast Discussion Number 1

2017-08-06 22:36:58| National Hurricane Center (Atlantic)

Issued at 500 PM EDT Sun Aug 06 2017 000 WTNT42 KNHC 062036 TCDAT2 Potential Tropical Cyclone Seven Discussion Number 1 NWS National Hurricane Center Miami FL AL072017 500 PM EDT Sun Aug 06 2017 Surface and scatterometer data indicate that the broad area of low pressure over the northwestern Caribbean Sea still lacks a well-defined center of circulation. However, this system is likely to become a tropical storm before reaching the coast of the Yucatan Peninsula late tomorrow, and advisories are being initiated to enable the issuance of a tropical storm warning and watch for Yucatan and Belize respectively. The scatterometer pass and NOAA data buoy observations indicate that the maximum winds are near 30 kt. The disturbance has been experiencing westerly vertical shear due to a nearby upper-level low and this has been inhibiting development. Global model predictions show that this low will soon dissipate and an upper-level anticyclone will become established over the area. Therefore, strengthening is likely with the main impediment being interaction with land. The official intensity forecast is a little above the model consensus. It should be noted that the system could become a hurricane between 72 and 96 hours, i.e. prior to reaching the Gulf coast of Mexico. Since the center lacks definition, the initial location and motion are quite uncertain, and my best guess for the current motion is 290/10. The steering pattern for the disturbance/tropical cyclone is expected to be fairly straightforward and persistent for the next few days. A general west-northwestward track is expected to continue until landfall in mainland Mexico. The official track forecast is generally a blend of the latest GFS and ECMWF solutions. FORECAST POSITIONS AND MAX WINDS INIT 06/2100Z 15.6N 82.0W 30 KT 35 MPH...POTENTIAL TROP CYCLONE 12H 07/0600Z 16.6N 83.6W 35 KT 40 MPH...TROPICAL CYCLONE 24H 07/1800Z 18.0N 85.9W 45 KT 50 MPH 36H 08/0600Z 19.0N 88.0W 45 KT 50 MPH...INLAND 48H 08/1800Z 19.9N 90.1W 35 KT 40 MPH...INLAND 72H 09/1800Z 21.0N 93.8W 60 KT 70 MPH...OVER WATER 96H 10/1800Z 21.2N 97.8W 60 KT 70 MPH...INLAND 120H 11/1800Z...DISSIPATED $$ Forecaster Pasch

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