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Tropical Depression Nineteen-E Forecast Discussion Number 1

2018-09-19 16:55:52| National Hurricane Center (East Pacific)

Issued at 900 AM MDT Wed Sep 19 2018 365 WTPZ44 KNHC 191455 TCDEP4 Tropical Depression Nineteen-E Discussion Number 1 NWS National Hurricane Center Miami FL EP192018 Issued by the NWS Weather Prediction Center College Park MD 900 AM MDT Wed Sep 19 2018 Satellite images show that an area of low pressure has developed over the Gulf of California overnight within an inverted trough. This is also supported by 24-hour pressure falls of 3.7 mb at Loreto just west of its center at 1300 UTC. Microwave imagery shows curved convective banding features to the east and north of the center, suggesting organized convection. Therefore the system is being declared a tropical depression with 25-kt maximum sustained winds. Infrared imagery shows minimal vertical wind shear over the system, with a slight restriction to the outflow on its western side, which is confirmed by recent SHIPS output. However, the system has only 12 hours or less over water, and it is expected to move inland without significant strengthening. An upper-level trough moving into the western United States is expected to steer the depression north or north-northeast across the Gulf of California into northwest Mexico tonight, which is well advertised by the track guidance. The depression is expected to dissipate in the 24-36 hour time frame due to steep terrain. The main impact with the system is expected to be heavy rainfall, with 5-10 inch areal average amounts and local amounts to 15 inches leading to life-threatening flash flooding and landslides near the track of the depression. FORECAST POSITIONS AND MAX WINDS INIT 19/1500Z 26.3N 110.9W 25 KT 30 MPH 12H 20/0000Z 28.0N 110.7W 25 KT 30 MPH...INLAND 24H 20/1200Z 30.5N 109.5W 15 KT 15 MPH...POST-TROP/REMNT LOW 36H 21/0000Z...DISSIPATED $$ Forecaster Roth/Blake

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Post-Tropical Cyclone Joyce Forecast Discussion Number 26

2018-09-19 04:35:29| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Tue Sep 18 2018 630 WTNT45 KNHC 190235 TCDAT5 Post-Tropical Cyclone Joyce Discussion Number 26 NWS National Hurricane Center Miami FL AL102018 1100 PM AST Tue Sep 18 2018 During the past couple of days, Joyce had been producing patches of deep convection that would quickly shear off due to strong westerly winds aloft. Each convective burst appeared weaker than the previous one, and during the past 12-18 hours, the circulation has been nearly devoid of deep convection. Therefore, Joyce no longer meets the criteria of a tropical cyclone, and this is the last advisory issued by the National Hurricane Center on this system. The initial wind speed is held at 25 kt, in agreement with a recent ASCAT pass around 2200Z that showed maximum winds in the 20-25 kt range. The remnant low is expected to gradually weaken and ultimately dissipate in a couple of days due to dry and stable air, cool SSTs, and moderate to strong westerly shear. Joyce is moving south-southwestward at 7 kt on the east side of a low- to mid-level ridge. A turn to the southwest is expected on Wednesday as the ridge builds to the northeast of the cyclone, and that motion should continue until the remnant low dissipates. The NHC track forecast lies near the middle of the guidance envelope. FORECAST POSITIONS AND MAX WINDS INIT 19/0300Z 30.4N 27.9W 25 KT 30 MPH...POST-TROP/REMNT LOW 12H 19/1200Z 29.9N 28.7W 20 KT 25 MPH...POST-TROP/REMNT LOW 24H 20/0000Z 29.4N 29.9W 20 KT 25 MPH...POST-TROP/REMNT LOW 36H 20/1200Z 28.9N 31.5W 15 KT 15 MPH...POST-TROP/REMNT LOW 48H 21/0000Z...DISSIPATED $$ Forecaster Cangialosi

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Tropical Depression Joyce Forecast Discussion Number 25

2018-09-18 22:29:32| National Hurricane Center (Atlantic)

Issued at 500 PM AST Tue Sep 18 2018 812 WTNT45 KNHC 182029 TCDAT5 Tropical Depression Joyce Discussion Number 25 NWS National Hurricane Center Miami FL AL102018 Issued by the NWS Weather Prediction Center College Park MD 500 PM AST Tue Sep 18 2018 Deep convection has generally been on the wane during the past day or so near the center of Joyce, and it is getting very close to no longer having organized deep convection. With the decrease in overall organization, the initial wind speed is set to 25 kt. An environment of strong westerly vertical wind shear (30-40 kt) and marginal sea surface temperatures (around 25C) should cause Joyce to become a remnant low by late tonight or early Wednesday. This agrees well with the latest global model guidance, and the timing of remnant low status has been moved up to 12 hours (or less). The initial motion of Joyce continues to turn and is now south- southwestward (205 degrees at 6 kt). The depression is forecast to turn increasingly to the southwest and west as the central Atlantic ridge builds to the north. Model guidance, except the HWRF, is tightly clustered, so the new forecast track is essentially an update of the previous one, closest to the HCCA consensus model. FORECAST POSITIONS AND MAX WINDS INIT 18/2100Z 30.9N 27.8W 25 KT 30 MPH 12H 19/0600Z 30.2N 28.3W 20 KT 25 MPH...POST-TROP/REMNT LOW 24H 19/1800Z 29.6N 29.4W 20 KT 25 MPH...POST-TROP/REMNT LOW 36H 20/0600Z 29.1N 30.9W 15 KT 15 MPH...POST-TROP/REMNT LOW 48H 20/1800Z...DISSIPATED $$ Forecaster Campbell/Blake

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Tropical Depression Joyce Forecast Discussion Number 24

2018-09-18 16:31:50| National Hurricane Center (Atlantic)

Issued at 1100 AM AST Tue Sep 18 2018 960 WTNT45 KNHC 181431 TCDAT5 Tropical Depression Joyce Discussion Number 24 NWS National Hurricane Center Miami FL AL102018 Issued by the NWS Weather Prediction Center College Park MD 1100 AM AST Tue Sep 18 2018 Earlier in the morning, the low-level center of Joyce became decoupled from a small area of deeper convection. However, another convective burst has recently developed after 12Z closer to the low-level center. The initial intensity of Joyce was held at 30 kt based on a recent ASCAT pass, which showed an area of 25-30 kt winds on the north side of the circulation. The number of wind retrievals close to 30 kt was rather limited, so Joyce's winds should decrease below 30 kt when it eventually loses deep convection. The depression is in an environment with strong westerly vertical wind shear (30-40 kt) and marginal sea surface temperatures (around 25C), and thus the primary forecast question is when Joyce will succumb to the relatively hostile environment, lose deep convection and become a remnant low. The GFS and ECMWF models both show some deep convection lingering into tomorrow before warming upper-level temperatures and increasingly dry air aloft kill off any remaining convection. Therefore, the 12-hour forecast point maintains tropical depression status, and the 24-hour forecast point indicates a post-tropical system. The initial motion of Joyce is now more southerly (185 degrees at 7 kt), and it will begin to turn increasingly to the southwest and west as the central Atlantic ridge builds to the north. The new forecast track is essentially an update of the previous one, which was close to the TVCA and HCCA consensus models. Minor adjustments were made in the first 24 hours to account for a slightly faster observed motion to the south in the past 6-12 hours. FORECAST POSITIONS AND MAX WINDS INIT 18/1500Z 31.6N 27.4W 30 KT 35 MPH 12H 19/0000Z 30.6N 27.7W 25 KT 30 MPH 24H 19/1200Z 29.9N 28.7W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 20/0000Z 29.4N 29.9W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 20/1200Z 29.0N 31.5W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 21/1200Z...DISSIPATED $$ Forecaster Lamers/Blake

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Tropical Depression Joyce Forecast Discussion Number 22

2018-09-18 04:37:25| National Hurricane Center (Atlantic)

Issued at 1100 PM AST Mon Sep 17 2018 065 WTNT45 KNHC 180237 TCDAT5 Tropical Depression Joyce Discussion Number 22 NWS National Hurricane Center Miami FL AL102018 1100 PM AST Mon Sep 17 2018 Joyce remains a very resilient tropical cyclone. After an earlier burst of deep convection just east of the low-level center that has since dissipated, a new convective burst has developed just north of the center with a curved convective band trying to develop in the eastern semicircle. All of this convective activity has been occurring despite westerly 850-200-mb vertical wind shear of near 35 kt and in the presence of very dry mid-level air. The initial intensity is being maintained a 30 kt based on earlier 28-kt ASCAT wind data, and the fact that no significant change has occurred to Joyce's low-level appearance in satellite imagery. The initial motion estimate is now 155/06 kt. Joyce is forecast to move around the eastern periphery of a deep-layer ridge located across the eastern Atlantic to the southwest and west of the cyclone. This large-scale steering feature is expected to gradually turn Joyce toward the south overnight and on Tuesday, and then force the cyclone toward the southwest on Wednesday and Thursday. The new NHC track forecast is to the west of the previous advisory track, and lies near the middle of the guidance envelope close to a blend of the consensus models TVCA and HCCA. Convective development during the past 12 hours has been in large part due to the strong atmospheric instability created by very cold 200-mb temperatures near -57 deg C overlaying relatively warm ocean temperatures of 25.5 deg C. A contributing factor to the most recent convective development appears to be enhanced uplift caused by an approaching shortwave trough noted in water vapor imagery between 30W-35W longitude. The latter feature is forecast by most of the global models to cut off south of the Azores and become entangled with Joyce's circulation over the next few days, resulting in a sharp decrease in the vertical wind shear and an increase in atmospheric instability/CAPE by 48 h and beyond, which would aid convective development and re-strengthening. For now, however, the new intensity forecast continues the weakening trend of the previous advisories due to an abundance of very dry mid-level air being entrained into the circulation, which is expected to shut down convective development, causing Joyce to dissipate shortly after 72 h. However, confidence in this forecast scenario is not very high, and some adjustments may be required to subsequent forecasts once the 18/0000Z model guidance becomes available, especially since the GFS- and ECMWF-based SHIPS and LGEM intensity guidance maintains Joyce as a 30- to 35-kt tropical cyclone through the next 120 hours. FORECAST POSITIONS AND MAX WINDS INIT 18/0300Z 33.2N 27.3W 30 KT 35 MPH 12H 18/1200Z 32.4N 27.1W 30 KT 35 MPH 24H 19/0000Z 31.4N 27.6W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 19/1200Z 30.5N 28.7W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 20/0000Z 29.9N 29.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 72H 21/0000Z 29.2N 33.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 96H 22/0000Z...DISSIPATED $$ Forecaster Stewart

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