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Tropical Storm Greg Forecast Discussion Number 9

2017-07-19 16:42:48| Tropical Depression LIDIA

Issued at 900 AM MDT Wed Jul 19 2017

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Tropical Depression Eight-E Forecast Discussion Number 5

2017-07-19 16:41:49| National Hurricane Center (East Pacific)

Issued at 800 AM PDT Wed Jul 19 2017 000 WTPZ43 KNHC 191441 TCDEP3 Tropical Depression Eight-E Discussion Number 5 NWS National Hurricane Center Miami FL EP082017 800 AM PDT Wed Jul 19 2017 The center of the depression is challenging to locate this morning with lots of disorganized convection in the vicinity of the apparent center. Microwave data suggest it is on the northeast side of the convective mass, although it doesn't agree that well with the overnight ASCAT data. The initial position tries to keep continuity from the overnight advisory, since there was a direct ASCAT hit at 0600Z, but it may have to be revised when visible imagery is available. The initial wind speed is kept at 30 kt, based on a blend of the TAFB/SAB fixes. Unfortunately the forecast of the depression isn't any easier than locating it. Some binary interaction with the circulation of Tropical Storm Greg is likely over the next few days since the cyclones should be moving fairly close to one another. This pattern would probably steer the depression southwestward, then northwestward by day 3 as Greg passes to the north and begins to draw the depression closer to it. The specifics of this interaction, however, are impossible to determine at this range because it also depends on how strong and exactly where the two systems are. It is becoming increasingly likely that Greg will be the more dominant and stronger system, causing the depression to take a more southward track, and would potentially absorb the depression in 4-5 days. The official forecast is shifted southward in the short-term to account for the latest model guidance, but is fairly close to the previous forecast at the end of the period. The intensity forecast is also tricky because many of the global models suggest that there is a window of lower shear between when the northwesterly outflow-related shear from Fernanda weakens and shifts to easterly shear related to the circulation and outflow from Greg. Most of the guidance, however, does not respond much to the lower shear, suggesting little change in intensity during the next couple of days. The new intensity forecast remains close to the model consensus and the previous NHC prediction, though the cyclone does have a small chance to become a tropical storm. The majority of the global models are showing the depression degenerating into a trough by day 4 due to increasing shear and interaction with the circulation of Greg, so the NHC forecast follows suit. It should be noted that this is a very uncertain forecast due to the unusually high number of difficult-to-predict variables. FORECAST POSITIONS AND MAX WINDS INIT 19/1500Z 14.5N 121.1W 30 KT 35 MPH 12H 20/0000Z 14.0N 121.8W 30 KT 35 MPH 24H 20/1200Z 13.3N 122.6W 30 KT 35 MPH 36H 21/0000Z 12.6N 123.3W 30 KT 35 MPH 48H 21/1200Z 12.3N 123.6W 30 KT 35 MPH 72H 22/1200Z 13.0N 124.5W 25 KT 30 MPH 96H 23/1200Z...DISSIPATED $$ Forecaster Blake

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Hurricane Fernanda Forecast Discussion Number 31

2017-07-19 16:40:46| National Hurricane Center (East Pacific)

Issued at 800 AM PDT Wed Jul 19 2017 000 WTPZ41 KNHC 191440 TCDEP1 Hurricane Fernanda Discussion Number 31 NWS National Hurricane Center Miami FL EP062017 800 AM PDT Wed Jul 19 2017 While there are still occasional glimpses of the eye in infrared imagery, the convective cloud pattern of Fernanda continues to slowly decay. The initial intensity is thus reduced a little more, to 75 kt, based on a blend of various satellite intensity estimates. Water vapor imagery shows that the outflow is becoming restricted in the southwestern quadrant, which is a reflection of 10-15 kt of southwesterly vertical shear affecting the cyclone. The initial motion is 310/7. Fernanda is expected to turn west-northwest later today and continue this motion through 72 h as it is steered by a strong low- to mid-level ridge to the north. This ridge is forecast to persist after 72 h. However, the guidance becomes more divergent during that time, likely due to how quickly the various large-scale models weaken Fernanda. The NAVGEM and Canadian models, which weaken the cyclone quickly, show a generally westward motion of the remnants. The GFS and the HWRF, which maintain a stronger vortex, show a more northerly motion on the right side of the guidance envelope. The ECMWF is between these extremes, and this part of new track forecast is a little to the north of the ECMWF and a little south of the model consensus. Overall, the new forecast is little changed through 72 h, then nudged north of the previous forecast thereafter. Fernanda is expected to steadily weaken through the forecast period due to various combinations of cool sea surface temperatures, southwesterly to southerly shear, and dry air entrainment. Thus, the new forecast again follows the trend of the previous advisory and calls for Fernanda to weaken to a tropical storm in less than 24 h, a post-tropical low by 72 h, and a remnant low by 96 h. The new forecast is little changed from the previous forecast and lies close to the intensity consensus. It should be noted that the GFS and ECMWF show the possibility that Fernanda could interact with an upper-level trough north of the Hawaiian Islands in a way that could prolong its life as a tropical cyclone. Currently, the confidence in this happening is too low to justify a change to the forecast. FORECAST POSITIONS AND MAX WINDS INIT 19/1500Z 17.4N 135.5W 75 KT 85 MPH 12H 20/0000Z 17.9N 136.5W 65 KT 75 MPH 24H 20/1200Z 18.5N 138.0W 55 KT 65 MPH 36H 21/0000Z 19.0N 139.6W 45 KT 50 MPH 48H 21/1200Z 19.5N 141.3W 40 KT 45 MPH 72H 22/1200Z 20.5N 144.5W 35 KT 40 MPH...POST-TROPICAL 96H 23/1200Z 22.0N 149.0W 30 KT 35 MPH...POST-TROP/REMNT LOW 120H 24/1200Z 23.0N 153.5W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Beven

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Tropical Storm Greg Forecast Discussion Number 8

2017-07-19 10:58:17| Tropical Depression LIDIA

Issued at 300 AM MDT Wed Jul 19 2017

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Tropical Depression EIGHT-E Forecast Discussion Number 4

2017-07-19 10:58:17| National Hurricane Center (East Pacific)

Issued at 200 AM PDT Wed Jul 19 2017 000 WTPZ43 KNHC 190858 TCDEP3 Tropical Depression Eight-E Discussion Number 4 NWS National Hurricane Center Miami FL EP082017 200 AM PDT Wed Jul 19 2017 The overall convective pattern of the depression has changed little since the previous advisory and remains ragged looking. Cloud tops colder than -70C have persisted near and to the south of the low-level center, yielding satellite estimates of T2.5/35 kt from SAB and UW-CIMSS ADT. However, the intensity will remain at 30 kt for this advisory since a 0500Z ASCAT-B overpass indicated a few wind vectors of 27-28 kt in the southwestern quadrant. The initial motion estimate is 20/05 kt. There is no significant change to the previous track forecast or reasoning. The global and regional models are in decent agreement on the depression engaging in some weak binary interaction with the larger circulation of Tropical Storm Greg as the latter cyclone passes about 200 nmi to the north over the next few days. The new forecast track is similar to the previous advisory track and lies near the TVCN consensus model. The upper-level westerly outflow on the east of Hurricane Fernanda is expected to keep the depression in a moderate to strong vertical wind shear regime for the next couple of days. After that, northerly outflow from Greg should act to maintain unfavorable shear conditions across the depression, preventing any significant strengthening until the system dissipates by 96 hours. The new intensity forecast is identical to the previous advisory and follows the consensus model IVCN. FORECAST POSITIONS AND MAX WINDS INIT 19/0900Z 14.6N 120.8W 30 KT 35 MPH 12H 19/1800Z 14.3N 121.4W 30 KT 35 MPH 24H 20/0600Z 13.8N 122.1W 25 KT 30 MPH 36H 20/1800Z 13.3N 122.7W 25 KT 30 MPH 48H 21/0600Z 12.9N 123.1W 25 KT 30 MPH 72H 22/0600Z 13.2N 124.1W 25 KT 30 MPH 96H 23/0600Z...DISSIPATED $$ Forecaster Stewart

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