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Tropical Storm Kristy Forecast Discussion Number 6

2018-08-08 10:59:11| National Hurricane Center (East Pacific)

Issued at 200 AM PDT Wed Aug 08 2018 626 WTPZ43 KNHC 080859 TCDEP3 Tropical Storm Kristy Discussion Number 6 NWS National Hurricane Center Miami FL EP132018 200 AM PDT Wed Aug 08 2018 Satellite images indicate that Kristy is not well organized, with a dry slot wrapping around the northwestern side of the circulation. In addition the center is on the northwestern edge of an area of deep convection; an artifact of continued shear. A scatterometer pass revealed maximum winds of about 35 kt, which is a fair bit below the satellite estimates. The initial wind speed is held at a possibly generous 40 kt since convection has increased in the past few hours. Shear from an upper-level low to the north-northeast of Kristy is forecast is relax in a day or so, and by that time the cyclone will probably have mixed the current dry air intrusion. Thus some restrengthening is shown commencing beyond 24 hours. There is only a narrow window for intensification, however, since between 48-72 hours the SSTs should become rather marginal with a possible increase in a shear. The guidance has come down markedly from the last cycle, with most of the models surprisingly showing no increase in strength. This forecast will lower the winds about 10 kt from the previous one during days 1-4, but is still about 10 kt above the consensus at those time frames since the environment doesn't appear to be that hostile. No change has been made to the initial motion estimate of 285/7 kt. Kristy should turn northwestward by this evening and then northward late Thursday as a narrow ridge is eroded away to the north of the cyclone. While some binary interaction with Hurricane John is possible, it seems like Kristy will be steered toward John, then turn northwestward in about 96 hours due to weak ridging developing between the cyclones. Model guidance is coming into better agreement on this scenario, with the ECMWF and GFS solutions converging toward the model consensus. The latest NHC forecast is slow to a blend of the corrected-consensus guidance, and is very close to the previous NHC track forecast. FORECAST POSITIONS AND MAX WINDS INIT 08/0900Z 14.2N 128.5W 40 KT 45 MPH 12H 08/1800Z 14.8N 129.4W 40 KT 45 MPH 24H 09/0600Z 15.5N 130.2W 40 KT 45 MPH 36H 09/1800Z 16.4N 130.5W 45 KT 50 MPH 48H 10/0600Z 17.3N 130.5W 50 KT 60 MPH 72H 11/0600Z 19.5N 130.0W 50 KT 60 MPH 96H 12/0600Z 21.5N 130.5W 40 KT 45 MPH 120H 13/0600Z 23.0N 132.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Blake

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Hurricane John Forecast Discussion Number 11

2018-08-08 10:58:40| Tropical Depression LIDIA

Issued at 300 AM MDT Wed Aug 08 2018

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Tropical Storm Debby Forecast Discussion Number 4

2018-08-08 10:34:12| National Hurricane Center (Atlantic)

Issued at 500 AM AST Wed Aug 08 2018 588 WTNT44 KNHC 080834 TCDAT4 Tropical Storm Debby Discussion Number 4 NWS National Hurricane Center Miami FL AL042018 500 AM AST Wed Aug 08 2018 Over the past several hours, deep convection with cloud tops of -55 to -60 deg C has developed in the southeastern semicircle, with some of the convective tops covering the previously exposed low-level circulation center. In addition, outer banding features have dissipated, and an elongated upper-level anticyclone has developed over the cyclone. These convective- and synoptic-scale features indicate that Debby has made the transition from a subtropical to a tropical cyclone. The initial intensity of 40 kt is based on a blend of UW-CIMSS ADT and SATCON intensity estimates of 39 kt and 42 kt, respectively. Furthermore, the 34-kt wind radii and radius of maximum winds (RMW) were decreased significantly on this advisory based on ASCAT wind data. The initial motion estimate is now 015/08 kt. Debby has made the forecast turn toward the north-northeast, and a further turn toward the northeast is expected later today as the cyclone moves around the northwestern periphery of a deep-layer ridge and ahead of an approaching mid-level trough. The latest model guidance remains in good agreement on this developing track scenario, and the new NHC forecast track is similar to the previous advisory, and lies close to a blend of the track consensus models HCCA and FSSE. Debby will be moving along a tight sea-surface temperature (SST) gradient for the next 24-36 hours or so, with the northwestern half the circulation being over sub-25C SSTs and the southeastern semicircle being over warmer waters where convection could continue to develop. Given the relatively low vertical wind shear regime that the cyclone will be moving through, along with the possibility of deep convection persisting near the center, the intensity forecast calls for little change in strength today, followed by only slight weakening tonight and early Thursday. By Thursday night or early Friday, SSTs beneath the cyclone are expected to decrease to near 20 deg C and the shear is forecast to increase to more than 20 kt, an unfavorable combination that should result in Debby dissipating over the far north Atlantic by 48 hours. FORECAST POSITIONS AND MAX WINDS INIT 08/0900Z 40.8N 48.8W 40 KT 45 MPH 12H 08/1800Z 41.8N 48.2W 40 KT 45 MPH 24H 09/0600Z 43.2N 46.1W 35 KT 40 MPH 36H 09/1800Z 44.5N 43.4W 30 KT 35 MPH 48H 10/0600Z...DISSIPATED $$ Forecaster Stewart

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Tropical Storm Kristy Forecast Discussion Number 5

2018-08-08 04:32:10| National Hurricane Center (East Pacific)

Issued at 800 PM PDT Tue Aug 07 2018 165 WTPZ43 KNHC 080232 TCDEP3 Tropical Storm Kristy Discussion Number 5 NWS National Hurricane Center Miami FL EP132018 800 PM PDT Tue Aug 07 2018 Kristy has become a little less organized this evening. An upper tropospheric low situated to the northeast of Kristy is producing moderate northwesterly shear which has degraded the cyclone's cloud pattern. A 2035 UTC AMSR2 overpass revealed that the surface center was partially exposed to the north of the convective banding features. The subjective Dvorak intensity estimates from TAFB and SAB have decreased as well, so the initial intensity for this advisory is lowered to 40 kt. Statistical and global models all show the upper low to the northeast of Kristy weakening and lifting out in 24 hours or so, which should provide a more conducive upper wind environment for intensification, at least through mid-period. Afterwards, a weakening trend should commence due to an intruding drier/stable air mass and cooler oceanic sea surface temperatures. The HWRF and HCCA show Kristy becoming a hurricane in 48 hours, which still seems quite reasonable and is reflected in the forecast. All of the other guidance reaches just below 65 kt. The NHC intensity forecast is based primarily on these two models, and indicates a peak intensity of 65 kt in 48 hours. The initial motion is estimated to be 285/7 kt, and Kristy is being steered by a narrow mid-level ridge to the northeast. A complex synoptic steering pattern comprised of an approaching deep-layer low pressure system to the northwest of the tropical storm, and John to the northeast, is forecast by most of the global and regional models to weaken what's left of the ridge currently steering Kristy. The increasing weakness in the subtropical ridge should cause Kristy to turn northwestward and northward through day 4. At the end of the period, a gradual turn toward the northwest around the periphery of larger John's circulation. The ECMWF deterministic and ensemble models continue to be outliers in the aforementioned scenario due to less influence from the growing weakness to the north and significantly less binary interaction with John. The official forecast is similar to the previous one, with a slight adjustment to the right and is basically in the middle of the HCCA and TVCE consensus models. FORECAST POSITIONS AND MAX WINDS INIT 08/0300Z 14.2N 127.8W 45 KT 50 MPH 12H 08/1200Z 14.6N 128.7W 45 KT 50 MPH 24H 09/0000Z 15.4N 129.6W 50 KT 60 MPH 36H 09/1200Z 16.4N 130.0W 60 KT 70 MPH 48H 10/0000Z 17.2N 130.1W 65 KT 75 MPH 72H 11/0000Z 19.5N 129.9W 60 KT 70 MPH 96H 12/0000Z 22.0N 130.6W 50 KT 60 MPH 120H 13/0000Z 24.3N 133.0W 30 KT 35 MPH...POST-TROP/REMNT LOW $$ Forecaster Roberts

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Subtropical Storm Debby Forecast Discussion Number 3

2018-08-08 04:31:08| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Tue Aug 07 2018 542 WTNT44 KNHC 080231 TCDAT4 Subtropical Storm Debby Discussion Number 3 NWS National Hurricane Center Miami FL AL042018 1100 PM AST Tue Aug 07 2018 A little bit of deep convection has developed near the center of Debby, but the overall cloud pattern still resembles more of a subtropical cyclone. Most of the convection is in a ragged band well to the northeast of the center. The initial intensity is held at 35 kt based on a subtropical ST2.5 classification from TAFB. The global models are in good agreement that the system will open up into a trough on the southern side of a large low pressure system within 48 hours. The initial motion estimate is a slightly slower 360/11 kt. Debby is likely to turn northeastward in the flow on the eastern side of a mid-level trough. The official forecast is somewhat faster than the latest model consensus to maintain some continuity with the previous NHC track. FORECAST POSITIONS AND MAX WINDS INIT 08/0300Z 40.3N 49.1W 35 KT 40 MPH 12H 08/1200Z 41.2N 48.9W 35 KT 40 MPH 24H 09/0000Z 42.5N 47.5W 35 KT 40 MPH 36H 09/1200Z 43.9N 44.7W 30 KT 35 MPH 48H 10/0000Z...DISSIPATED $$ Forecaster Pasch

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