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Tropical Storm Henriette Forecast Discussion Number 5

2019-08-13 04:50:35| National Hurricane Center (East Pacific)

Issued at 900 PM MDT Mon Aug 12 2019 000 WTPZ44 KNHC 130250 TCDEP4 Tropical Storm Henriette Discussion Number 5 NWS National Hurricane Center Miami FL EP092019 900 PM MDT Mon Aug 12 2019 Scatterometer data and visible satellite imagery indicate that Henriette has maintained a robust, compact low-level circulation despite the pulsing convection. In fact, three earlier ASCAT passes between 1613Z and 1728Z indicated reliable wind speeds of 37-38 kt, suggesting that Henriette could have been near 40 kt prior to those times. However, since 1800Z, northeasterly vertical wind shear and dry air intrusions have reduced and confined the overall convective pattern to just intermittent bursts in the southwestern quadrant. The initial intensity is being maintained at 35 kt based on the shear pattern, a UW-CIMSS ADT intensity estimate of T2.4/34 kt, and allowing for some slight spin down of the low-level vortex. The initial motion remains 290/11 kt. A west-northwestward motion is forecast to continue for the next 24 hours so, followed by a turn toward the west by early Wednesday as the weakening cyclone becomes vertically shallow and gets steered by the low-level easterly tradewind flow. The new NHC forecast track remains essentially unchanged and is just an extension of the previous advisory, and lies about midway between the consensus models HCCA and TVCE. Although the official intensity forecast calls for steady weakening, it is possible that Henriette could remain a tropical storm in 12 h due to the cyclone coming out of the convective maximum period and still located over SSTs between 26C and 26.5 deg C. However, by 18 h and beyond, the cyclone will be moving over sub-26C SSTs and into a drier environment, which is expected to result in significant weakening, with Henriette degenerating into a remnant low by late Tuesday and dissipating by late Wednesday. The official intensity forecast is identical to previous advisory and closely follows the IVCN and HCCA consensus intensity forecast models. FORECAST POSITIONS AND MAX WINDS INIT 13/0300Z 20.7N 114.3W 35 KT 40 MPH 12H 13/1200Z 21.2N 116.0W 30 KT 35 MPH 24H 14/0000Z 21.8N 118.4W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 14/1200Z 22.3N 121.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 15/0000Z...DISSIPATED $$ Forecaster Stewart

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Tropical Storm Henriette Forecast Discussion Number 4

2019-08-12 22:52:33| National Hurricane Center (East Pacific)

Issued at 300 PM MDT Mon Aug 12 2019 000 WTPZ44 KNHC 122052 TCDEP4 Tropical Storm Henriette Discussion Number 4 NWS National Hurricane Center Miami FL EP092019 300 PM MDT Mon Aug 12 2019 Dry air and northeasterly shear have been steadily eroding the deep convection around the center of Henriette today. The low-level center is exposed and the only deep convection remaining is confined to the western semicircle. Despite the degradation in the satellite presentation, a recent ASCAT pass showed that tropical- storm- force winds are still occuring in a small area near the center of the compact storm. Based on this data, the initial intensity remains 35 kt. The initial motion is 290/11 kt. This motion will continue through tonight while the cyclone is steered by a mid-level ridge to its north. A turn to the west is expected on Tuesday as the system weakens and becomes steered by the low-level flow. The official forecast is very near the previous one, and is close to the corrected consensus HCCA which lies on the southern side of the other consensus aids. Dry, stable air and ongoing shear should limit convection over the cyclone while the circulation remains over marginally favorable SSTs. This lack of convection should cause a weakening trend to commence very soon. By Tuesday, Henriette will move over SSTs below 26 C, which, combined with the other unfavorable environmental conditions, should cause the cyclone to degenerate into a remnant low by late Tuesday. The official forecast calls for a little faster weakening of Henriette than the previous one, and is near the various multi-model consensus solutions. FORECAST POSITIONS AND MAX WINDS INIT 12/2100Z 20.3N 113.1W 35 KT 40 MPH 12H 13/0600Z 20.9N 114.8W 30 KT 35 MPH 24H 13/1800Z 21.6N 117.1W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 14/0600Z 22.1N 119.7W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 14/1800Z...DISSIPATED $$ Forecaster Latto/Pasch

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Tropical Storm Henriette Forecast Discussion Number 3

2019-08-12 16:33:30| National Hurricane Center (East Pacific)

Issued at 900 AM MDT Mon Aug 12 2019 000 WTPZ44 KNHC 121433 TCDEP4 Tropical Storm Henriette Discussion Number 3 NWS National Hurricane Center Miami FL EP092019 900 AM MDT Mon Aug 12 2019 Henriette is a sheared tropical cyclone, with microwave and first-light visible satellite imagery revealing a low level center that is near the northeastern edge of the deep convection. The overall presentation of the cyclone has changed little over the past several hours, and therefore the initial intensity is being held at 35 kt. This is in agreement with an earlier ASCAT pass showing a very small area of 30-35 kt winds over the northwestern portion of the circulation. The initial motion is 295/10 kt. Henriette is expected to continue this general motion for the next 24 hours as it is steered by a mid-level ridge that extends from northern Mexico to the north of the cyclone. A turn to the west is expected on Tuesday as the system weakens and becomes steered by the low-level flow. The official forecast is slightly south of the previous one through 24 hours, due to a more southward initial position. Beyond 24 hours, the official forecast is very near the previous one, and near the middle of the consensus aids. Northeasterly shear and dry air over the northern portion of the cyclone should continue to keep the low level center near the edge of the deep convection into tonight, preventing any further strengthening. By 24 hours, the cyclone is forecast to cross the 26 C SST isotherm and move into a more stable airmass. This should cause the cyclone to lose its convection and weaken on Tuesday, with the system likely becoming a remnant low by Tuesday night. The official intensity forecast is close to the previous one, and is in agreement with the various dynamical and consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 12/1500Z 19.7N 112.2W 35 KT 40 MPH 12H 13/0000Z 20.2N 113.9W 35 KT 40 MPH 24H 13/1200Z 20.9N 116.1W 30 KT 35 MPH 36H 14/0000Z 21.4N 118.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 14/1200Z...DISSIPATED $$ Forecaster Latto/Pasch

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Tropical Storm Henriette Forecast Discussion Number 2

2019-08-12 10:36:28| National Hurricane Center (East Pacific)

Issued at 300 AM MDT Mon Aug 12 2019 000 WTPZ44 KNHC 120836 TCDEP4 Tropical Storm Henriette Discussion Number 2 NWS National Hurricane Center Miami FL EP092019 300 AM MDT Mon Aug 12 2019 Deep convection has continued to burst over the western portion of the cyclone overnight. Although the system is sheared with the center located near the northeastern edge of the convective mass, a couple of ASCAT passes have shown a very small area of 30-35 kt winds over the northwestern portion of the circulation. These winds extend no more than about 15-20 n mi from the center, but based on these data the initial wind speed has been increased to 35 kt. Henriette becomes the eighth named storm in the eastern Pacific basin this season. The ASCAT data also assisted in locating the center this morning, and recent fixes show that Henriette continues to move west- northwestward or 295/12 kt. The tropical storm should move west-northwestward around the southwestern portion of a deep-layer ridge that extends westward from northern Mexico. As Henriette weakens, it is likely to turn westward within the low-level flow. The updated NHC track forecast is similar to the previous advisory through 36 hours, but has been adjusted southward at 48 hours to be closer to the various consensus aids. Henriette is not anticipated to strengthen much more. Although the system is predicted to remain over warm waters and within an area of light to moderate northeasterly shear today, nearby dry mid-level air is likely to prevent significant strengthening. By Tuesday morning, Henriette will be moving over cooler waters and into a more stable airmass. This should lead to weakening, and the cyclone is predicted to degenerate into a remnant low within 48 hours, with dissipation occurring shortly thereafter. FORECAST POSITIONS AND MAX WINDS INIT 12/0900Z 19.5N 110.9W 35 KT 40 MPH 12H 12/1800Z 20.2N 112.4W 35 KT 40 MPH 24H 13/0600Z 21.0N 114.4W 35 KT 40 MPH 36H 13/1800Z 21.7N 116.8W 30 KT 35 MPH 48H 14/0600Z 22.0N 120.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 15/0600Z...DISSIPATED $$ Forecaster Brown

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Tropical Depression Nine-E Forecast Discussion Number 1

2019-08-12 04:51:54| National Hurricane Center (East Pacific)

Issued at 900 PM MDT Sun Aug 11 2019 000 WTPZ44 KNHC 120251 TCDEP4 Tropical Depression Nine-E Discussion Number 1 NWS National Hurricane Center Miami FL EP092019 900 PM MDT Sun Aug 11 2019 The broad low pressure system that the NHC has been tracking the past several days has finally developed a well-defined surface circulation and enough organized deep convection to be classified as a tropical depression. A late-arriving 1716Z ASCAT-C scatterometer pass indicated the surface wind field was possibly closed at that time, but since then deep convection with tops of -75C to -80C have persisted near and to the west of the mid-level circulation center, suggesting that a low-level center has likely closed off now. Dvorak satellite intensity estimates are T1.5/25 kt from both TAFB and SAB, but the initial intensity is set at 30 kt based on 30-31 kt winds indicated in the aforementioned scatterometer data. The initial motion is estimated to be west-northwestward or 295/12 kt, based primarily on scatterometer and passive microwave fixes. The small cyclone is expected to move west-northwestward around the southern periphery of a deep-layer ridge for the next 3 days until dissipation occurs. The NHC track forecast lies near the southern portion of the guidance envelope, between the TVCE consensus model and the ECMWF-ensemble mean model. The small cyclone only has about 36 hours to strengthen before the system moves over sub-26 deg C SSTs. The shear is forecast to be low at less than 10 kt for the next 72 hours or so, even decreasing to near 5 kt in 24-36 h, which would normally result in significant development. However, intermittent intrusions of dry mid-level air are expected to disrupt the typical intensification process, thus only modest strengthening is forecast through 36 h, after which much cooler waters will induce a weakening trend. The official intensity forecast closely follows a blend of the HCCA and IVCN intensity consensus models. FORECAST POSITIONS AND MAX WINDS INIT 12/0300Z 18.9N 109.8W 30 KT 35 MPH 12H 12/1200Z 19.4N 111.2W 35 KT 40 MPH 24H 13/0000Z 20.3N 113.1W 35 KT 40 MPH 36H 13/1200Z 21.3N 115.3W 35 KT 40 MPH 48H 14/0000Z 22.1N 117.8W 30 KT 35 MPH...POST-TROP/REMNT LOW 72H 15/0000Z 23.7N 123.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 96H 16/0000Z...DISSIPATED $$ Forecaster Stewart

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