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Tropical Depression NINE Forecast Discussion Number 12

2016-08-31 16:43:22| National Hurricane Center (Atlantic)

Issued at 1000 AM CDT WED AUG 31 2016 000 WTNT44 KNHC 311442 TCDAT4 TROPICAL DEPRESSION NINE DISCUSSION NUMBER 12 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092016 1000 AM CDT WED AUG 31 2016 The system is producing vigorous deep convection, but there is little organization to the overall cloud pattern. Using the Dvorak rules, a bursting but disorganized convective pattern would indicate little change in strength. The intensity is held at 30 kt pending new observations from a NOAA Hurricane Hunter aircraft in a few hours. The tropical cyclone should be in a moderate shear environment, and over very warm water, for the next 36 hours or so. Therefore, strengthening is forecast and the official forecast remains close to the intensity model consensus. Given the reasonably favorable environment, it is appropriate to maintain the hurricane watch for the northeast Gulf coast at this time. The intensity forecast after 48 hours is problematic since the system will be in a decidedly baroclinic environment and under strong upper-level southwesterly flow. This means that any intensification that occurs in 2-3 days will likely have a contribution from baroclinic processes. By 96 hours, the global models depict the system as embedded in a frontal zone, so extratropical transition is forecast to occur by that time. The center is very difficult to locate, but observations from a ship suggest that there has been little motion since earlier this morning, so the initial motion estimate is stationary. There has been little change to the track forecast guidance. A 500-mb trough over the southeastern United States should cause the cyclone to move north-northeastward to northeastward across northern Florida and southeastern Georgia during the next couple of days. Later in the forecast period there is uncertainty as to how far offshore the center will move, with some of the global models such as the GFS and the U.K. Met being close to the northeastern states, and the ECMWF somewhat farther east. The official track forecast lies between these two possibilities. It is important not to focus on the forecast landfall point of this system. Among other reasons, dangerous storm surge flooding is likely to extend along the Gulf coast well to the east and south of the path of the center. FORECAST POSITIONS AND MAX WINDS INIT 31/1500Z 24.6N 88.0W 30 KT 35 MPH 12H 01/0000Z 25.9N 87.4W 40 KT 45 MPH 24H 01/1200Z 27.3N 86.5W 45 KT 50 MPH 36H 02/0000Z 29.0N 85.0W 55 KT 65 MPH 48H 02/1200Z 30.9N 82.4W 50 KT 60 MPH...INLAND 72H 03/1200Z 35.0N 75.0W 55 KT 65 MPH...OVER WATER 96H 04/1200Z 38.0N 70.0W 55 KT 65 MPH...POST-TROP/EXTRATROP 120H 05/1200Z 40.0N 69.0W 55 KT 65 MPH...POST-TROP/EXTRATROP $$ Forecaster Pasch

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Hurricane LESTER Forecast Discussion Number 28

2016-08-31 16:38:16| National Hurricane Center (East Pacific)

Issued at 800 AM PDT WED AUG 31 2016 000 WTPZ43 KNHC 311438 TCDEP3 HURRICANE LESTER DISCUSSION NUMBER 28 NWS NATIONAL HURRICANE CENTER MIAMI FL EP132016 800 AM PDT WED AUG 31 2016 The convective ring around Lester's eye has warmed and shrunk a little in the past couple of hours, but the 15-20 n mi wide eye remains distinct. Based on a blend of the latest subjective and objective Dvorak estimates, the initial intensity is set to 115 kt for this advisory. The forecast environment of low shear, marginally cool SSTs, and a drier mid-level environment should result in weakening during the next couple of days. Later in the period the SSTs remain marginal, but southeasterly shear increases, and this should result in continued weakening through the rest of the forecast period. This trend is seen in all of the intensity guidance, with some spread. The NHC intensity forecast has been adjusted downward a bit this cycle. This forecast is above the latest IVCN intensity consensus aid through 48 hours and near the consensus at days 3-5. The initial motion estimate is 270/10. Lester will continue to be steered westward and then turn west-northwestward by an expansive mid-level ridge extending across much of the central and eastern Pacific Ocean through the forecast period. The track model guidance is in generally good agreement on this scenario, however, there remains some significant across-track spread in the guidance near the Hawaiian Islands. The UKMET and GEFS ensemble mean are along the southern edge of the guidance envelope with a track closer to the Big Island, while the HWRF and GFDL are farther north of the island chain. The ECMWF, GFS, and consensus aids lie between these scenarios just north of the islands. The new NHC forecast is largely an update of the previous one and lies between the multi- model consensus and the latest GFS track. All interests in the Hawaiian Islands should continue to monitor the progress of Lester, as it is too early to determine what impacts there could be along the island chain from this tropical cyclone given the track forecast uncertainty in 3 to 5 days. FORECAST POSITIONS AND MAX WINDS INIT 31/1500Z 17.8N 138.6W 115 KT 130 MPH 12H 01/0000Z 17.9N 140.3W 110 KT 125 MPH 24H 01/1200Z 18.1N 142.4W 105 KT 120 MPH 36H 02/0000Z 18.6N 144.7W 95 KT 110 MPH 48H 02/1200Z 19.2N 147.2W 85 KT 100 MPH 72H 03/1200Z 20.6N 152.5W 70 KT 80 MPH 96H 04/1200Z 22.5N 157.5W 60 KT 70 MPH 120H 05/1200Z 24.5N 162.5W 55 KT 65 MPH $$ Forecaster Brennan

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Hurricane LESTER Forecast Discussion Number 27

2016-08-31 10:59:03| National Hurricane Center (East Pacific)

Issued at 200 AM PDT WED AUG 31 2016 000 WTPZ43 KNHC 310858 TCDEP3 HURRICANE LESTER DISCUSSION NUMBER 27 NWS NATIONAL HURRICANE CENTER MIAMI FL EP132016 200 AM PDT WED AUG 31 2016 Lester continues to display a distinct 20 nm diameter eye in the middle of a symmetric eyewall with no banding features. Subjective Dvorak classifications from SAB and TAFB remain at 6.5 and 6.0 current intensity numbers, respectively, while the CIMSS Advanced Dvorak Technique is at 6.6. A blend of these gives 120 kt maximum winds at the initial time, the same as previously indicated. Lester is anticipated to experience quite low vertical shear for the next few days, though the lukewarm SSTs and about 40 percent humidity air are only marginally conducive for maintaining high intensities. The current convective structure and its environment suggest that Lester may have evolved into an annular hurricane, which tends to weaken only slowly over time. The 00Z intensity model guidance has backed off some from the 18Z model suite. The NHC intensity forecast - slightly lower than that in the previous advisory - is closest to the SHIPS model through 48 hours and the HWRF thereafter. Lester is moving toward the west at about 10 kt. A large subtropical ridge to its north is providing the westward steering and low shear environment. The tightly packed model guidance indicate that the system should turn slightly toward the west-northwest during the next few days at about the same rate of forward speed. The NHC track forecast is based upon the TVCN multi-model consensus technique and is slightly south of the track from the previous advisory. A 0604Z ASCAT scatterometer pass indicated little change was needed for the initial 34- and 50-kt wind radii. The NHC wind radii forecast is based upon the RVCN consensus technique and nearly the same as that from the last advisory. FORECAST POSITIONS AND MAX WINDS INIT 31/0900Z 17.7N 137.5W 120 KT 140 MPH 12H 31/1800Z 17.7N 139.1W 115 KT 130 MPH 24H 01/0600Z 18.0N 141.3W 110 KT 125 MPH 36H 01/1800Z 18.3N 143.5W 100 KT 115 MPH 48H 02/0600Z 18.9N 145.8W 90 KT 105 MPH 72H 03/0600Z 20.2N 151.0W 75 KT 85 MPH 96H 04/0600Z 21.8N 156.0W 65 KT 75 MPH 120H 05/0600Z 24.0N 161.0W 60 KT 70 MPH $$ Forecaster Landsea

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Tropical Depression EIGHT Forecast Discussion Number 12

2016-08-31 10:54:49| National Hurricane Center (Atlantic)

Issued at 500 AM EDT WED AUG 31 2016 000 WTNT43 KNHC 310854 TCDAT3 TROPICAL DEPRESSION EIGHT DISCUSSION NUMBER 12 NWS NATIONAL HURRICANE CENTER MIAMI FL AL082016 500 AM EDT WED AUG 31 2016 The low-level center is difficult to find, but given the strong westerly shear and continuity, it is assumed that it is located to the west of a large area of deep convection devoid of banding features. Dvorak numbers have not changed, and the initial intensity remains at 30 kt. Most of the guidance shows a significant increase in the shear, but at the same time forecasts a slight increase in intensity. The NHC forecast follows the guidance and the previous forecast showing a slight increase in the winds before the cyclone becomes extratropical in 48 hours. The depression is moving slowly toward the northeast at 4 kt, and is already embedded within the southwesterly flow ahead of an amplifying mid-latitude trough. This pattern favors a continuation of the northeast track away from the U.S coast with a significant increase in forward speed. FORECAST POSITIONS AND MAX WINDS INIT 31/0900Z 34.8N 74.3W 30 KT 35 MPH 12H 31/1800Z 35.7N 72.8W 35 KT 40 MPH 24H 01/0600Z 37.7N 69.0W 40 KT 45 MPH 36H 01/1800Z 40.0N 63.5W 40 KT 45 MPH 48H 02/0600Z 42.5N 57.5W 35 KT 40 MPH...POST-TROP/EXTRATROP 72H 03/0600Z...DISSIPATED $$ Forecaster Avila

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Tropical Depression NINE Forecast Discussion Number 11

2016-08-31 10:53:07| National Hurricane Center (Atlantic)

Issued at 400 AM CDT WED AUG 31 2016 000 WTNT44 KNHC 310852 TCDAT4 TROPICAL DEPRESSION NINE DISCUSSION NUMBER 11 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092016 400 AM CDT WED AUG 31 2016 Although clusters of deep convection continue to pulsate near and to the southeast of the center of the tropical cyclone, there has been little overall change in organization overnight. A couple of ASCAT passes since the previous advisory revealed peak winds of 30 kt, so the system remains a 30-kt tropical depression for this advisory. The upper-level outflow has expanded to the northwest and north of the cyclone, which suggests that the upper-level wind pattern is becoming more favorable for strengthening. The SHIPS model indicates that the shear should remain low during the next day or so, while the cyclone moves over warm water. This should allow for strengthening, and the NHC forecast calls for steady intensification during the next day or so, which is also supported by the global models. The updated intensity forecast is in good agreement with the multi-model consensus. The depresssion has been meandering overnight, but is expected to begin a northward or northeastward motion later today. A deepening trough over the southeastern United States should cause the tropical cyclone to accelerate north-northeastward or northeastward by tonight. Although the track guidance is in good agreement on this scenario, the model envelope has shifted slightly westward this cycle, and the NHC forecast track has been nudged in that direction. The new forecast has required the issuance of a Tropical Storm Warning for a portion of the Florida Gulf coast. The Hurricane Watch remains in effect since there is still a possibility that the system could become a hurricane before landfall. It is important not to focus on the forecast landfall point of this system. Among other reasons, dangerous storm surge flooding is likely along the coast well to the east and south of the path of the center. FORECAST POSITIONS AND MAX WINDS INIT 31/0900Z 24.5N 88.1W 30 KT 35 MPH 12H 31/1800Z 25.4N 87.8W 40 KT 45 MPH 24H 01/0600Z 26.9N 86.9W 45 KT 50 MPH 36H 01/1800Z 28.4N 85.6W 55 KT 65 MPH 48H 02/0600Z 30.3N 83.6W 55 KT 65 MPH...INLAND 72H 03/0600Z 34.2N 76.8W 60 KT 70 MPH...OVER WATER 96H 04/0600Z 37.0N 70.2W 60 KT 70 MPH 120H 05/0600Z 39.0N 68.0W 55 KT 65 MPH...POST-TROP/EXTRATROP $$ Forecaster Brown

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