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Tropical Storm Hector Forecast Discussion Number 7

2018-08-02 10:49:22| National Hurricane Center (East Pacific)

Issued at 200 AM PDT Thu Aug 02 2018 853 WTPZ45 KNHC 020849 TCDEP5 Tropical Storm Hector Discussion Number 7 NWS National Hurricane Center Miami FL EP102018 200 AM PDT Thu Aug 02 2018 Hector's satellite presentation has quickly improved over the past few hours. Recent microwave and scatterometer data indicate that the low-level center is now well embedded within the expanding convective canopy, and a tiny mid-level eye has formed. In fact, a late-arriving WindSat pass from around 0230 UTC showed that Hector had a mid-level structure that has been associated with rapidly intensifying tropical cyclones, when present in low-shear environments. The initial intensity has been raised to 60 kt based on a timely ASCAT-B overpass around 0556 UTC. Although the maximum winds measured by the ASCAT were only around 55 kt, at least some undersampling seems likely given the small size of the inner-core of the cyclone. The northeasterly shear that has been affecting Hector does not appear to be significantly affecting the inner-core of the cyclone at this time. However, it is uncertain whether this is only a short-term trend, or if the inner core will remain protected from the higher shear going forward. While the GFS and ECMWF indicate that the shear should decrease through today, the HWRF and HMON models forecast that Hector will become strongly sheared by tomorrow and temporarily weaken as a result. The small size of the tropical cyclone further complicates the intensity forecast since small cyclones can quickly intensify or weaken, especially in moderate shear environments, and these short-term fluctuations are very difficult to predict. As a course of least regret, the NHC forecast does not show significant strengthening or weakening for the first 48 h of the forecast and instead shows steady strengthening, similar to the DSHP and LGEM models, and is higher than the previous advisory. For days 3-5, there is a better consensus among the models that Hector will strengthen, and the official forecast is still close to the multi-model consensus and the previous forecast. The initial motion estimate is now 285/10 kt. There is more confidence in the track forecast. A strong subtropical ridge extending from the eastern Pacific into the central Pacific should keep Hector on a general west heading through the entire forecast period. The main source of uncertainty is still the speed of the tropical cyclone at days 3-5. Since the main difference between the models appears to be subtle differences in the strength of the ridge, the NHC forecast is still based on the multi-model consensus and little change has been made from the previous advisory. FORECAST POSITIONS AND MAX WINDS INIT 02/0900Z 14.3N 123.4W 60 KT 70 MPH 12H 02/1800Z 14.5N 125.1W 65 KT 75 MPH 24H 03/0600Z 14.6N 127.4W 70 KT 80 MPH 36H 03/1800Z 14.5N 129.7W 75 KT 85 MPH 48H 04/0600Z 14.4N 132.0W 80 KT 90 MPH 72H 05/0600Z 14.0N 136.6W 85 KT 100 MPH 96H 06/0600Z 14.0N 141.5W 95 KT 110 MPH 120H 07/0600Z 14.5N 146.5W 95 KT 110 MPH $$ Forecaster Zelinsky

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Tropical Storm Hector Forecast Discussion Number 6

2018-08-02 04:36:24| National Hurricane Center (East Pacific)

Issued at 800 PM PDT Wed Aug 01 2018 691 WTPZ45 KNHC 020236 TCDEP5 Tropical Storm Hector Discussion Number 6 NWS National Hurricane Center Miami FL EP102018 800 PM PDT Wed Aug 01 2018 Visible satellite imagery continues to show an increase in banding in association with Hector, and the last several images suggest that a small CDO may be developing. Recent microwave data, however, has not shown any significant improvement of the inner core. The latest Dvorak satellite estimates are 45 kt from SAB and 55 kt from TAFB, while AMSU and objective UW/CIMSS Dvorak estimates are in between. As a result, the initial wind speed has been increased to 50 kt. An increase in northeasterly shear by tomorrow is expected to temporarily halt the intensification process. However, the shear is expected to decrease after 48 hours, which should allow for strengthening later in the period while Hector remains over warm water. There is still a large spread in the intensity guidance by day 4, with the ECMWF-based SHIPS guidance showing an intensity of around 65 kt, while the HWRF and COAMPS-TC model bring Hector to category 4 strength. Given the large divergence in the intensity guidance at the long range, the NHC forecast remains close to the consensus aids. Hector continues to move westward at around 10 kt. There has been no significant change to the track forecast reasoning. Hector should move generally westward to the south of a strong subtropical ridge through Friday. The ridge is forecast to build westward by the weekend which is expected to impart a west-southwestward motion through the remainder of the forecast period. The overall track guidance envelope has not changed since the previous advisory and the NHC track forecast is near the middle of the envelope. The latest NHC track prediction is very close to the previous NHC advisory. FORECAST POSITIONS AND MAX WINDS INIT 02/0300Z 14.0N 122.2W 50 KT 60 MPH 12H 02/1200Z 14.3N 124.0W 55 KT 65 MPH 24H 03/0000Z 14.4N 126.3W 60 KT 70 MPH 36H 03/1200Z 14.5N 128.6W 60 KT 70 MPH 48H 04/0000Z 14.5N 131.0W 65 KT 75 MPH 72H 05/0000Z 14.0N 135.8W 80 KT 90 MPH 96H 06/0000Z 13.5N 140.5W 90 KT 105 MPH 120H 07/0000Z 13.8N 145.0W 90 KT 105 MPH $$ Forecaster Brown

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Tropical Storm Hector Forecast Discussion Number 5

2018-08-01 22:37:51| National Hurricane Center (East Pacific)

Issued at 200 PM PDT Wed Aug 01 2018 384 WTPZ45 KNHC 012037 TCDEP5 Tropical Storm Hector Discussion Number 5 NWS National Hurricane Center Miami FL EP102018 200 PM PDT Wed Aug 01 2018 Hector continues to become better organized. Microwave data indicate that the low- and mid-level centers are now closer together, and visible satellite imagery is showing more curved banding features. Dvorak estimates from TAFB, SAB and the CIMSS ADT are all 45 kt, so that will be the initial intensity. Hector should continue to intensify for the next day or so in a favorable environment of light-to-moderate shear and warm SSTs. However, a surge of northeasterly upper-level flow is forecast to impact the cyclone on Thursday, which will likely arrest the strengthening trend. This stronger flow should abate late Friday or Saturday, leading to further intensification. The latest forecast is below the consensus at shorter range, then above the consensus at long range. There remains the potential that the intensity forecast is too low at days 4 and 5, but the model guidance is too divergent with the upper-level environment at that time to have confidence in raising the forecast. Scatterometer and microwave data are showing the system moving westward at 10 kt. Hector should continue moving westward overnight and then even move a little south-of-west for the next few days as the subtropical ridge builds to the north and west of the cyclone. The biggest change from 6 hours ago is that the guidance is faster at long range due to the tropical cyclone staying separate from an upper-level trough in the northwestward part of the eastern Pacific. The latest NHC forecast follows the speedier trend of the guidance, but is not as fast as the ECMWF or UKMET models. FORECAST POSITIONS AND MAX WINDS INIT 01/2100Z 13.8N 121.2W 45 KT 50 MPH 12H 02/0600Z 14.1N 122.8W 55 KT 65 MPH 24H 02/1800Z 14.4N 125.1W 60 KT 70 MPH 36H 03/0600Z 14.5N 127.4W 60 KT 70 MPH 48H 03/1800Z 14.5N 129.7W 65 KT 75 MPH 72H 04/1800Z 14.1N 134.6W 80 KT 90 MPH 96H 05/1800Z 13.5N 139.3W 90 KT 105 MPH 120H 06/1800Z 13.5N 143.5W 90 KT 105 MPH $$ Forecaster Blake

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Tropical Storm Hector Forecast Discussion Number 4

2018-08-01 16:46:17| National Hurricane Center (East Pacific)

Issued at 800 AM PDT Wed Aug 01 2018 479 WTPZ45 KNHC 011446 TCDEP5 Tropical Storm Hector Discussion Number 4 NWS National Hurricane Center Miami FL EP102018 800 AM PDT Wed Aug 01 2018 Satellite images indicate that Hector is on a strengthening trend, with a large area of convection near and west of the apparent center. The latest microwave data, a 1159Z F-16 pass, also show the beginnings of an inner core in the 91-Ghz channels. The system has some tilt, however, with suggestions from the microwave pass that the low- and mid-level centers are not well aligned. The latest intensity estimates from TAFB/SAB are 45 kt, but I've elected to only raise the wind speed to 40 kt due to uncertainty in the initial position and the microwave tilt. Hector is forecast to remain over warm water, with light-to- moderate shear and somewhat dry mid-level moisture for the next several days. In 12 to 24 hours, northeasterly shear is forecast to increase near Hector, which should slow the intensification rate. Thus the official forecast shows strengthening at less than a climatological rate for the next few days. At long range, some of model guidance suggest the upper-level environment could become very favorable, with the HWRF/HMON now showing Hector at category 4 strength in the central Pacific Ocean. I would prefer to see more consistency from these models before showing such a large increase, but the new forecast is raised from the previous one and is higher than the model consensus. The storm is moving west-northwestward at 11 kt. Hector should turn to the west tomorrow and even move a little south-of-west for the next few days thereafter as the subtropical ridge builds to the north and west of the cyclone. The largest uncertainty is the location of Hector in a few days as an inverted upper-level trough forms to the north or northeast of the cyclone. For now there is enough separation of Hector and this trough to prevent the cyclone from gaining much latitude. While the model guidance doesn't show a lot of spread for now, and the new forecast is close to the previous one, it is worth keeping an eye on the trough to make sure it stays separate from Hector at long range. FORECAST POSITIONS AND MAX WINDS INIT 01/1500Z 13.8N 120.4W 40 KT 45 MPH 12H 02/0000Z 14.2N 122.0W 50 KT 60 MPH 24H 02/1200Z 14.5N 124.1W 55 KT 65 MPH 36H 03/0000Z 14.6N 126.4W 60 KT 70 MPH 48H 03/1200Z 14.5N 128.7W 65 KT 75 MPH 72H 04/1200Z 14.4N 133.5W 75 KT 85 MPH 96H 05/1200Z 13.9N 138.2W 90 KT 105 MPH 120H 06/1200Z 13.7N 142.0W 90 KT 105 MPH $$ Forecaster Blake

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Tropical Storm Hector Forecast Discussion Number 3

2018-08-01 10:32:43| National Hurricane Center (East Pacific)

Issued at 200 AM PDT Wed Aug 01 2018 120 WTPZ45 KNHC 010832 TCDEP5 Tropical Storm Hector Discussion Number 3 NWS National Hurricane Center Miami FL EP102018 200 AM PDT Wed Aug 01 2018 Hector is still somewhat disorganized, with a majority of its deep convection displaced to the south and west of its surface center. In fact, a recent AMSU pass around 0515 UTC indicated that the center of Hector was nearly exposed on the northeast side of a small curved band. Dvorak classifications from TAFB and SAB have not changed since the last advisory and the ASCAT instruments missed the cyclone once again, so the initial intensity has been held at 35 kt. Easterly shear of around 10 kt, as analyzed in SHIPS diagnostics, appears to be the primary factor preventing Hector from becoming better organized. The latest GFS and ECMWF runs at 00Z suggest that the shear will increase slightly during the next 24-36 hours before decreasing substantially during the second half of the forecast period. Despite the shear, all of the intensity guidance forecasts that Hector will intensify in an otherwise favorable environment, and the intensity guidance is generally higher than it was previously. The dynamical hurricane models, HWRF, HMON, and COAMPS-TC all bring Hector to near major hurricane strength, while SHIPS and LGEM are a little lower. Given that Hector is still fairly disorganized, the intensity forecast for the first 24 hours is somewhat conservative, and favors the statistical-dynamical models. Beyond that time, the NHC intensity forecast is a little higher than it was previously, but is still just below the intensity consensus. The estimated initial motion of the tropical storm is 285/13 kt. Little change has been made to the track forecast, which has been adjusted only slightly to the north through most of the forecast period. The track guidance is in very good agreement on the track of Hector, and the main source of uncertainty is the speed at which an extensive mid-level ridge to the north will steer the cyclone westward. Since I see no obvious reason to favor any one of the typically-reliable global models, the NHC forecast is now very close to the various consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 01/0900Z 13.4N 119.4W 35 KT 40 MPH 12H 01/1800Z 13.9N 121.1W 40 KT 45 MPH 24H 02/0600Z 14.2N 123.2W 50 KT 60 MPH 36H 02/1800Z 14.4N 125.2W 60 KT 70 MPH 48H 03/0600Z 14.4N 127.5W 65 KT 75 MPH 72H 04/0600Z 14.3N 132.0W 75 KT 85 MPH 96H 05/0600Z 14.0N 136.0W 80 KT 90 MPH 120H 06/0600Z 14.0N 140.0W 80 KT 90 MPH $$ Forecaster Zelinsky

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