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Tropical Storm Gert Forecast Discussion Number 7
2017-08-14 16:38:32| National Hurricane Center (Atlantic)
Issued at 1100 AM EDT Mon Aug 14 2017 000 WTNT43 KNHC 141438 TCDAT3 Tropical Storm Gert Discussion Number 7 NWS National Hurricane Center Miami FL AL082017 1100 AM EDT Mon Aug 14 2017 Gert has become better organized this morning. A recent 1336 UTC GMI overpass shows a large band of convection wrapping around the circulation from the southwest to the northwest quadrant. However, imagery from the GMI overpass, as well as an earlier SSMIS overpass, suggest that the mid-level center is displaced somewhat south or southeast of the low-level center, due to continued northerly shear of about 15 kt. Based on the improved structure and increased subjective Dvorak classifications from TAFB and SAB, the initial intensity has been raised to 50 kt. Gert is now moving toward the north, and the initial motion estimate is 360/07 kt. Very little change has been made to the track forecast. Gert should continue to move around the western periphery of the subtropical ridge for the next day or so, before rapidly accelerating eastward ahead of a trough. Since Gert has already turned northward, the NHC forecast is on the eastern side of the guidance envelope for the first 48 h, but very near the multi-model consensus after that time. Despite the presence of moderate northerly vertical wind shear, there is good agreement among the intensity guidance that Gert will continue to strengthen for the next 48 h. The HWRF is an outlier in showing Gert becoming a major hurricane around that time, while DSHP, LGEM, and CTCI only forecast modest intensification. Since SHIPS diagnostics from the GFS and ECMWF suggest that the shear will never decrease below 10 kt, the NHC forecast gives more weight to the modest intensification scenario. All of the global models show extratropical transition (ET) beginning around 48 h, and completing by about 72 h. After ET completes, Gert is still expected to steadily weaken before being absorbed by a larger extratropical low in about 4 or 5 days. The 72 h and 96 h track, intensity, and wind radii forecasts incorporated guidance from the Ocean Prediction Center. FORECAST POSITIONS AND MAX WINDS INIT 14/1500Z 30.3N 72.2W 50 KT 60 MPH 12H 15/0000Z 31.5N 72.2W 55 KT 65 MPH 24H 15/1200Z 33.4N 71.3W 60 KT 70 MPH 36H 16/0000Z 35.8N 68.8W 65 KT 75 MPH 48H 16/1200Z 38.4N 64.0W 70 KT 80 MPH 72H 17/1200Z 43.0N 50.0W 65 KT 75 MPH...POST-TROP/EXTRATROP 96H 18/1200Z 50.0N 36.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 19/1200Z...DISSIPATED $$ Forecaster Zelinsky
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Tropical Storm Gert Forecast Discussion Number 6
2017-08-14 10:34:50| National Hurricane Center (Atlantic)
Issued at 500 AM EDT Mon Aug 14 2017 000 WTNT43 KNHC 140834 TCDAT3 Tropical Storm Gert Discussion Number 6 NWS National Hurricane Center Miami FL AL082017 500 AM EDT Mon Aug 14 2017 Although Gert's asymmetric convective cloud pattern has improved slightly since the previous advisory, the system remains sheared with the low-level center located near the far northwestern edge of the deepest convection due to deep-layer and mid-level northerly shear of 15 kt. Although the satellite intensity estimates are a consensus T3.0/45 kt from TAFB, SAB, and UW-CIMSS ADT, the initial intensity is being held at 40 kt due to the low-level center having become more exposed since those 0600 UTC intensity estimates. Gert has maintained a north-northwestward motion or 345/08 kt. There are significant changes to the previous track forecast or reasoning. The small cyclone is expected to turn northward shortly and then turn toward the north-northeast by tonight, moving through a break in the subtropical ridge roughly midway between the U.S. east coast and Bermuda on Tuesday. By 48 h, Gert is forecast to steadily accelerate northeastward over the north Atlantic through the remainder of the forecast period ahead of a strong deep-layer trough. The latest guidance has again shifted a little bit to the west after recurvature, so the official forecast was nudged in that direction slightly, but remains on the far eastern edge of the guidance envelope. Gert should continue to be affected by moderate northerly vertical wind shear and dry mid-level air for the next 24-30 h, so only slight strengthening is anticipated despite the very warm SSTs beneath the cyclone. By 36-48h, a window of opportunity for more significant strengthening is expected when the shear decreases to less than 10 kt after the cyclone begins to recurve, with Gert possibly becoming a hurricane by 48 h. However, the intensification trend is expected to be short-lived due to the vertical wind shear shifting to southwesterly and increasing to more than 30 kt by 60 h and beyond. By 72 h, Gert will be moving over ocean temperatures of 20 deg C and colder, which should induce and sustain extratropical transition. Gert's intensity is held to near-hurricane strength at 72 h due to the system getting a baroclinic kick when the cyclone moves underneath a favorable region of the upper-level jetstream. However, rapid weakening is expected by 96 h when the cyclone is moving over 15 deg C SSTs, with the system being absorbed on day 5 by a larger extratropical low pressure system over the far north Atlantic. The official intensity forecast is similar to the previous advisory, and is lower than the consensus models IVCN and HCCA. This is due to the HWRF model creating a high bias in those models caused by an unrealistic forecast of Gert becoming a category 4 hurricane in 72 h when the cyclone will be moving over SSTs of 25 deg C or colder and in shear conditions greater than 35-40 kt. FORECAST POSITIONS AND MAX WINDS INIT 14/0900Z 29.7N 72.2W 40 KT 45 MPH 12H 14/1800Z 30.9N 72.3W 45 KT 50 MPH 24H 15/0600Z 32.7N 71.9W 50 KT 60 MPH 36H 15/1800Z 34.9N 70.0W 55 KT 65 MPH 48H 16/0600Z 37.3N 66.0W 65 KT 75 MPH 72H 17/0600Z 42.7N 52.1W 60 KT 70 MPH...POST-TROP/EXTRATROP 96H 18/0600Z 49.0N 38.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 19/0600Z...ABSORBED BY LARGER EXTRATROPICAL LOW $$ Forecaster Stewart
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Post-Tropical Cyclone Jova Forecast Discussion Number 9
2017-08-14 04:31:50| Tropical Depression LIDIA
Issued at 800 PM PDT Sun Aug 13 2017
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Tropical Depression Jova Forecast Discussion Number 8
2017-08-13 22:33:20| Tropical Depression LIDIA
Issued at 200 PM PDT Sun Aug 13 2017
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Tropical Storm Gert Forecast Discussion Number 4
2017-08-13 22:32:18| National Hurricane Center (Atlantic)
Issued at 500 PM EDT Sun Aug 13 2017 000 WTNT43 KNHC 132032 TCDAT3 Tropical Storm Gert Discussion Number 4 NWS National Hurricane Center Miami FL AL082017 500 PM EDT Sun Aug 13 2017 Satellite images indicate that the tropical cyclone is gradually strengthening. The banding features have become better established during the last several hours, and the system has become less vertically tilted. The Dvorak classification from TAFB and ADT values from CIMSS at the University of Wisconsin support increasing the initial wind speed to 35 kt, making the system Tropical Storm Gert. Gert is moving north-northwestward at 9 kt on the southwestern periphery of a subtropical ridge. A northward motion is expected tonight and Monday while the system rounds the western side of the ridge, and Gert is expected to be about midway between Bermuda and North Carolina on Monday and Tuesday. After that time, a progressively faster motion to the northeast and east-northeast is forecast as the system moves on the north side of the ridge and becomes embedded in the mid-latitude westerlies until it dissipates in about 5 days. The track guidance remains in very good agreement, and only small changes were made to the previous NHC prediction. This forecast lies near the middle of the tightly clustered guidance envelope. The system is over warm 29 deg C SSTs, and it will remain over these warm waters during the next few days. In addition, the global models indicate that the upper-level pattern should become conducive for strengthening during the next 36 hours or so. The combination of these conditions should allow Gert to strengthen during the next couple of days. Thereafter, a sharp increase in west-southwesterly shear, drier air, and decreasing sea surface temperatures should end the strengthening trend and lead to extratropical transition in a little more than 3 days. The NHC intensity forecast is slightly above the previous one, but remains on the lower side of the guidance. The center of Gert recently passed very near NOAA buoy 41047, and that data has been helpful in estimating the minimum pressure of the system. FORECAST POSITIONS AND MAX WINDS INIT 13/2100Z 28.1N 71.7W 35 KT 40 MPH 12H 14/0600Z 29.3N 72.1W 40 KT 45 MPH 24H 14/1800Z 31.1N 72.1W 50 KT 60 MPH 36H 15/0600Z 32.9N 71.3W 55 KT 65 MPH 48H 15/1800Z 35.1N 68.8W 55 KT 65 MPH 72H 16/1800Z 39.8N 59.1W 50 KT 60 MPH 96H 17/1800Z 45.0N 44.5W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 18/1800Z...DISSIPATED $$ Forecaster Cangialosi
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