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Tropical Depression Gilma Forecast Discussion Number 10

2018-07-29 04:35:19| National Hurricane Center (East Pacific)

Issued at 800 PM PDT Sat Jul 28 2018 882 WTPZ43 KNHC 290235 TCDEP3 Tropical Depression Gilma Discussion Number 10 NWS National Hurricane Center Miami FL EP082018 800 PM PDT Sat Jul 28 2018 Gilma's structure has not changed much over the past six hours. Deep convection remains limited to small, but frequent, bursts just east of the depression's exposed low-level center. The initial intensity has been held at 30 kt, based primarily on continuity, but this is also supported by the most recent Dvorak classification from TAFB. No change has been made to the official intensity forecast. The wind shear, as measured in SHIPS diagnostic data from the GFS and ECMWF, is already over 30 kt and is forecast to continue increasing over the next day or two. In addition, the tropical cyclone will be moving through a progressively drier environment during the next couple of days, which should also contribute to the suppression of deep convection. Gilma is therefore still forecast to become a remnant low tomorrow, and then dissipate entirely by early next week. The depression is moving a little quicker than previously anticipated, and the initial motion estimate is 285/12. Aside from the faster initial speed, there is no change to the reasoning behind the track forecast. Gilma is still expected to turn back toward the west and slow its forward speed for the next couple of days while being steered primarily by the low-level flow associated with the subtropical ridge to the north. The NHC track forecast is very close to the various consensus models, and minimal changes were made from the previous advisory. FORECAST POSITIONS AND MAX WINDS INIT 29/0300Z 16.1N 135.7W 30 KT 35 MPH 12H 29/1200Z 16.3N 137.2W 30 KT 35 MPH 24H 30/0000Z 16.4N 139.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 30/1200Z 16.3N 141.4W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 31/0000Z 16.1N 143.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 01/0000Z...DISSIPATED $$ Forecaster Zelinsky

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Tropical Depression Gilma Forecast Discussion Number 9

2018-07-28 22:32:17| National Hurricane Center (East Pacific)

Issued at 200 PM PDT Sat Jul 28 2018 372 WTPZ43 KNHC 282032 TCDEP3 Tropical Depression Gilma Discussion Number 9 NWS National Hurricane Center Miami FL EP082018 200 PM PDT Sat Jul 28 2018 Increasing westerly shear is taking its toll on Gilma. Deep convection that has been persisting on the eastern side of the system has become farther separated from the center, with an exposed low-level swirl centered more than 75 n mi from the edge of the convection. Although the system appears to be a little weaker than earlier today, there is no scatterometer data to confirm that. Therefore, the initial wind speed has been held at 30 kt, in agreement with the Dvorak classifications of 2.0/30 kt from both TAFB and SAB. Westerly shear of about 30 to 35 kt is expected to continue during the next few days, and the global models indicate that the upper-level flow should become less diffluent as Gilma passes west of the axis of an upper-level trough tonight. The combination of these hostile winds aloft, cooler SSTs, and a more stable air mass should cause Gilma to gradually weaken, and the NHC forecast now shows Gilma becoming a remnant low in about 24 hours and degenerating into a trough by day 4. Gilma could become a remnant low even sooner than currently forecast, as the unfavorable upper-level flow to the west of the upper trough axis could completely shear off the deep convection from the center. The depression made a jog to the northwest during the day today, but it is expected to resume a west to west-northwestward motion at around 10 kt through tonight, steered by mid-level ridging to the north. Thereafter, as the system becomes increasingly shallow, it should turn to the west, steered by low-level ridging to its northwest. The NHC forecast track is very close to the previous forecast, and it is close to the clustering of the consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 28/2100Z 15.8N 134.3W 30 KT 35 MPH 12H 29/0600Z 16.0N 135.6W 30 KT 35 MPH 24H 29/1800Z 16.3N 137.4W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 30/0600Z 16.3N 139.6W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 30/1800Z 16.1N 141.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 31/1800Z 15.7N 145.8W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 01/1800Z...DISSIPATED $$ Forecaster Cangialosi/Latto

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Tropical Depression Gilma Forecast Discussion Number 8

2018-07-28 16:32:44| National Hurricane Center (East Pacific)

Issued at 800 AM PDT Sat Jul 28 2018 708 WTPZ43 KNHC 281432 TCDEP3 Tropical Depression Gilma Discussion Number 8 NWS National Hurricane Center Miami FL EP082018 800 AM PDT Sat Jul 28 2018 Despite being in an environment of strong westerly shear, Gilma is maintaining its status as a tropical cyclone. Deep convection has been persisting on the eastern side of the system, and this activity has even moved a little closer to the center, aided by upper-level diffluence. The initial wind speed is held at 30 kt, in agreement with the Dvorak classifications of 2.0/30 kt from TAFB and SAB. This intensity estimate is a little lower than the 2.5/35 kt ADT values from CIMSS at the University of Wisconsin. Westerly shear of about 30 kt is likely to continue during the next few days, and the global models indicate that the upper-level flow should become less diffluent as Gilma approaches the Central Pacific basin. These hostile winds aloft combined with cooler SSTs and a more stable air mass should cause Gilma to gradually weaken during the next few days. The NHC forecast continues to show Gilma becoming a remnant low in about 36 hours and degenerating into a trough by day 4, following the trend in the model guidance. The depression is moving westward at 10 kt steered by the flow on the south side of a mid-level ridge. A west to west-northwest motion is expected during the next few days as the increasingly shallow system moves within the low- to mid-level flow. The NHC track forecast is a little south of the previous one to come into better agreement with the latest consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 28/1500Z 15.2N 133.0W 30 KT 35 MPH 12H 29/0000Z 15.4N 134.3W 30 KT 35 MPH 24H 29/1200Z 15.7N 136.0W 25 KT 30 MPH 36H 30/0000Z 15.8N 137.9W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 30/1200Z 15.7N 140.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 31/1200Z 15.4N 144.4W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 01/1200Z...DISSIPATED $$ Forecaster Cangialosi

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Tropical Depression Gilma Forecast Discussion Number 7

2018-07-28 10:35:14| National Hurricane Center (East Pacific)

Issued at 200 AM PDT Sat Jul 28 2018 640 WTPZ43 KNHC 280835 TCDEP3 Tropical Depression Gilma Discussion Number 7 NWS National Hurricane Center Miami FL EP082018 200 AM PDT Sat Jul 28 2018 Gilma continues to be affected by strong westerly vertical shear, with the low level center remaining exposed to the northwest of an area of weakly banded convection. Satellite intensity estimates are in the 25-35 kt range, so the initial intensity remains a possibly generous 30 kt. The initial motion is 280/11. The low- to mid-level subtropical ridge to the north of the cyclone should continue steering the cyclone generally westward to west-northwestward for the next three days with some decrease in forward speed. The new track forecast is similar to the previous forecast and lies a little to the north of the center of the guidance envelope and the various consensus models. The ongoing shear is due to an upper-level trough just to the west and northwest of the tropical cyclone. The dynamical models suggest that this trough will move westward in close proximity to Gilma, which will allow the shear to continue. In addition, the cyclone should be moving into a drier airmass during the next several days. These factors should cause Gilma to weaken and eventually dissipate during the forecast period even though it will stay over warm water. The new intensity forecast is mostly an update of the previous forecast, and it now calls for Gilma to decay to a remnant low by 36 h and dissipate completely after 72 h. FORECAST POSITIONS AND MAX WINDS INIT 28/0900Z 15.1N 132.4W 30 KT 35 MPH 12H 28/1800Z 15.4N 133.9W 25 KT 30 MPH 24H 29/0600Z 16.0N 135.7W 25 KT 30 MPH 36H 29/1800Z 16.3N 137.4W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 30/0600Z 16.4N 139.3W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 31/0600Z 16.5N 143.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 01/0600Z...DISSIPATED $$ Forecaster Beven

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Tropical Depression Gilma Forecast Discussion Number 6

2018-07-28 04:36:44| National Hurricane Center (East Pacific)

Issued at 800 PM PDT Fri Jul 27 2018 023 WTPZ43 KNHC 280236 TCDEP3 Tropical Depression Gilma Discussion Number 6 NWS National Hurricane Center Miami FL EP082018 800 PM PDT Fri Jul 27 2018 The satellite presentation of Gilma has not changed much over the past several hours. Strong west-northwesterly shear continues to affect tropical cyclone, and deep convection is limited to the southeast quadrant of the otherwise exposed low-level circulation. The initial intensity has been held at 30 kt based on earlier ASCAT data, but recent Dvorak intensity estimates from TAFB and SAB suggest this could be generous. Virtually no change has been made to the track or intensity forecasts. All of the dynamical models indicate that the shear affecting Gilma will increase through the next several days, and the cyclone will be moving into a drier environment. Continued weakening is therefore still forecast, in line with all of the intensity guidance. While the NHC forecast currently shows that Gilma will be a closed low through 72 hours, it is entirely possible that Gilma will dissipate sooner than currently indicated due to the hostile environment. As expected, Gilma has slowed slightly and the initial motion estimate is now 280/13 kt. A continued west to west-northwest heading with a decrease in forward speed is still forecast for the next few days while the shallow depression is steered primarily by the low-level flow associated with the subtropical high to the north-northeast. The NHC forecast remains in close agreement with the various track consensus models. FORECAST POSITIONS AND MAX WINDS INIT 28/0300Z 15.0N 131.3W 30 KT 35 MPH 12H 28/1200Z 15.2N 132.7W 30 KT 35 MPH 24H 29/0000Z 15.7N 134.5W 25 KT 30 MPH 36H 29/1200Z 16.2N 136.2W 25 KT 30 MPH 48H 30/0000Z 16.5N 138.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 31/0000Z 16.5N 142.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 01/0000Z...DISSIPATED $$ Forecaster Zelinsky

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