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Tropical Depression One Forecast Discussion Number 1

2020-05-16 22:39:25| National Hurricane Center (Atlantic)

Issued at 500 PM EDT Sat May 16 2020 000 WTNT41 KNHC 162039 TCDAT1 Tropical Depression One Discussion Number 1 NWS National Hurricane Center Miami FL AL012020 500 PM EDT Sat May 16 2020 Satellite images, Doppler radar data, and surface observations indicate that the low pressure system located just east of the coast of central Florida has developed sufficient organization to now be classified as a tropical depression. The low-level center is well defined and deep convection has persisted near the center and in bands on the east side of the circulation for the past several hours. The cyclone is considered tropical instead of subtropical because it has central deep convection and a relatively small radius of maximum wind. The initial intensity is estimated to be 30 kt based on data collected earlier today by the Air Force Hurricane Hunters. Another aircraft is scheduled to investigate the system this evening. Based on satellite data and the earlier reconnaissance fixes, the initial motion of the system is north-northeastward at 11 kt. A continued north-northeastward motion at about the same forward speed is expected during the next 24 hours or so, keeping the cyclone offshore, but parallel to, the east coast of Florida. After that time, the model solutions begin to diverge and the details of the track forecast become more complicated. The important features for the future track of the depression appear to be a pair of mid- to upper-level troughs currently over the central U.S. The specific amplitude, timing, and location of those troughs will ultimately result in how close to the coast of North Carolina this system gets. The GFS and HWRF models are on the left side of the guidance and bring the system inland or along the coast, while the ECMWF and UKMET models show an offshore track. The NHC track forecast splits the difference of these solutions, and lies close to the various consensus models, which usually perform best. It should be noted that forecast uncertainty is typically larger for weak systems like this one. The system should gradually strengthen during the next couple of days as it remains over the Gulf Stream current and in relatively low wind shear conditions. However, the surrounding air mass is not particularly moist, so that and the marginally warm SSTs should limit significant intensification. The NHC intensity forecast calls for the system to become a tropical storm tonight or on Sunday with continued slow strengthening as it nears the North Carolina coast. Extratropical transition should occur in about 3 days, or sooner. The NHC intensity forecast generally lies roughly near the middle of the guidance envelope. Key Messages: 1. A tropical storm watch has been issued for a portion of the North Carolina coast. Tropical-storm-force winds and heavy rains are possible there on Monday. 2. Dangerous coastal surf conditions and rip currents are expected to spread northward from Florida to the mid-Atlantic states during the next few days. See products from your local National Weather Service for more details. FORECAST POSITIONS AND MAX WINDS INIT 16/2100Z 28.4N 78.6W 30 KT 35 MPH 12H 17/0600Z 29.7N 78.0W 35 KT 40 MPH 24H 17/1800Z 31.4N 77.4W 35 KT 40 MPH 36H 18/0600Z 33.0N 76.6W 40 KT 45 MPH 48H 18/1800Z 35.2N 74.8W 45 KT 50 MPH 60H 19/0600Z 37.1N 72.3W 50 KT 60 MPH 72H 19/1800Z 38.0N 70.0W 50 KT 60 MPH...POST-TROP/EXTRATROP 96H 20/1800Z 38.0N 68.5W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 21/1800Z...DISSIPATED $$ Forecaster Cangialosi

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Post-Tropical Cyclone One-E Forecast Discussion Number 6

2020-04-26 22:35:34| National Hurricane Center (East Pacific)

Issued at 200 PM PDT Sun Apr 26 2020 000 WTPZ41 KNHC 262035 TCDEP1 Post-Tropical Cyclone One-E Discussion Number 6 NWS National Hurricane Center Miami FL EP012020 200 PM PDT Sun Apr 26 2020 The cyclone has lacked significant organized deep convection for at least 10 hours, and the system is moving into increasingly more stable air and over sub-25C deg C SSTs. Therefore, the depression has been downgraded to a post-tropical remnant low. The initial intensity is 25 kt is based on several 23-25 kt wind vectors located n-e of the low-level center in a 1718 UTC ASCAT-A overpass. Although the system may still produce some sporadic convection late tonight during the convective maximum period, dry and stable air along with strong westerly shear will likely prevent any appreciable convection from persisting over the next day or so. This should cause the remnant low to weaken and then open up into a trough in 36-48 hours. The initial motion remains 305/08 kt. A substantial low- to mid-level ridge to the north of the cyclone is expected to gradually nudge the shallow low toward the west-northwest later this afternoon, followed by a westward motion tonight, with that motion continuing until the system dissipates Monday night. The new NHC track forecast is essentially just an update of the previous advisory track. This is the last advisory issued by the National Hurricane Center on this system. For additional information on the remnant low, please see High Seas Forecasts issued by the National Weather Service, under AWIPS header NFDHSFEPI, WMO header FZPN02 KWBC, and on the web at ocean.weather.gov/shtml/NFDHSFEPI.php . FORECAST POSITIONS AND MAX WINDS INIT 26/2100Z 16.2N 119.4W 25 KT 30 MPH...POST-TROPICAL 12H 27/0600Z 16.7N 120.9W 20 KT 25 MPH...POST-TROP/REMNT LOW 24H 27/1800Z 17.1N 122.9W 20 KT 25 MPH...POST-TROP/REMNT LOW 36H 28/0600Z 17.3N 125.1W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 28/1800Z...DISSIPATED $$ Forecaster Stewart

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Tropical Depression One-E Forecast Discussion Number 5

2020-04-26 16:38:52| National Hurricane Center (East Pacific)

Issued at 800 AM PDT Sun Apr 26 2020 000 WTPZ41 KNHC 261438 TCDEP1 Tropical Depression One-E Discussion Number 5 NWS National Hurricane Center Miami FL EP012020 800 AM PDT Sun Apr 26 2020 Deep convection has been waning quickly in the southeastern quadrant since the previous advisory, and the system barely met Dvorak criteria for identifying it as a tropical cyclone at 1200 UTC. Given that the 0446 UTC ASCAT-A overpass mentioned in the previous discussion revealed a fairly sizable area of 28-30 kt winds in the northeastern quadrant, there might be one or two 30-kt vectors remaining despite the recent decline in the convective pattern, and thus the intensity has been held at 30 kt for this advisory. The initial motion remains northwestward, or 305/08 kt. A strong subtropical ridge to the north of the depression is expected to gradually turn the cyclone toward the west-northwest later today and then westward by tonight, with a westward motion being maintained thereafter until the system dissipates by late Monday. The new NHC track forecast is essentially just an extension of the previous advisory track, and lies close to the tightly packed consensus track models Deep-layer dry air and cooler sea-surface temperatures, combined with strong westerly shear of 25-30 kt, should continue to erode what little bit of convection remains, causing the system to rapidly degenerate into a remnant low by this afternoon or evening. The low is then expected to dissipate by Monday night. The new intensity forecast is similar to the previous advisory, and closely follows the intensity consensus models IVCN and HCCA. FORECAST POSITIONS AND MAX WINDS INIT 26/1500Z 15.7N 118.8W 30 KT 35 MPH 12H 27/0000Z 16.3N 120.1W 25 KT 30 MPH...POST-TROP/REMNT LOW 24H 27/1200Z 16.8N 122.1W 20 KT 25 MPH...POST-TROP/REMNT LOW 36H 28/0000Z 17.0N 124.2W 20 KT 25 MPH...POST-TROP/REMNT LOW 48H 28/1200Z...DISSIPATED $$ Forecaster Stewart

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Tropical Depression One-E Forecast Discussion Number 4

2020-04-26 09:35:43| National Hurricane Center (East Pacific)

Issued at 200 AM PDT Sun Apr 26 2020 771 WTPZ41 KNHC 260735 TCDEP1 Tropical Depression One-E Discussion Number 4 NWS National Hurricane Center Miami FL EP012020 200 AM PDT Sun Apr 26 2020 Earlier NRL WindSAT microwave imagery and GOES16 ProxyVIS showed the depression's ill-defined center of circulation still displaced well to the northwest of a small, shapeless patch of deep convection. A 0446 UTC METOP-A scatterometer pass revealed a couple of 30 kt winds to the east of the surface center. Accordingly, the initial intensity is held at 30 kt. Low to mid-level drier air indicated by the SHIPS intensity guidance, and 20-25 kt of westerly shear shown in the UW-CIMSS shear product, are certainly prohibiting convective development. An intruding dry, stable air mass, increasing shear, and gradually decreasing sea surface temperatures should induce a weakening trend soon and ultimately cause the cyclone to become a remnant low by tonight. The large-scale and regional guidance all show the depression dissipating no later than Monday night. The initial motion is estimated to be northwestward, or 305/7 kt. A Low to mid-tropospheric ridge anchored north of the depression should influence a continued northwestward motion through today. Afterward, the cyclone is expected to degenerate into a shallow remnant low, and move westward in the low-level easterly flow until it dissipates. The new official forecast is similar to the previous advisory track, and is primarily based on the multi-model consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 26/0900Z 15.2N 118.2W 30 KT 35 MPH 12H 26/1800Z 15.9N 119.4W 30 KT 35 MPH 24H 27/0600Z 16.4N 121.2W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 27/1800Z 16.8N 123.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 28/0600Z...DISSIPATED $$ Forecaster Roberts

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Tropical Depression One-E Forecast Discussion Number 3

2020-04-26 04:32:14| National Hurricane Center (East Pacific)

Issued at 800 PM PDT Sat Apr 25 2020 000 WTPZ41 KNHC 260232 TCDEP1 Tropical Depression One-E Discussion Number 3 NWS National Hurricane Center Miami FL EP012020 800 PM PDT Sat Apr 25 2020 Deep convection has increased a little in association with Tropical Depression One-E during the past several hours. However, visible satellite images and an AMSR2 microwave pass from a few hours ago indicate that the low-level center is displaced to the northwest of the main area of showers and thunderstorms. The initial intensity is held at 30 kt, following the Dvorak classification from TAFB. This estimate is also in line with the latest satellite intensity estimates from CIMSS ADT and SATCON. It is also worth noting that dry air is wrapping into the circulation of the depression, which is likely limiting its convective organization. Although some very short-term strengthening can't be ruled out and it is possible that the cyclone could briefly become a tropical storm, weakening should begin on Sunday. The system will be moving into an environment of strong westerly shear, drier air, and progressively cooler waters. These conditions should cause the system to become a remnant low by Sunday night, when the shear is expected to be near 30 kt and SSTs around 24 C beneath the cyclone. All of the models show the the depression dissipating entirely early next week. The track forecast reasoning is unchanged from earlier today. The depression is currently moving northwestward on the southwest side of a mid-level ridge, and it should continue moving in that direction for the next 12 to 24 hours. After that time, the cyclone is forecast to be a shallow remnant low, and it expected to move westward in the low-level trade wind flow until it dissipates. The NHC track forecast lies near the middle of the guidance envelope. FORECAST POSITIONS AND MAX WINDS INIT 26/0300Z 14.8N 117.5W 30 KT 35 MPH 12H 26/1200Z 15.6N 118.6W 30 KT 35 MPH 24H 27/0000Z 16.3N 120.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 36H 27/1200Z 16.7N 122.3W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 28/0000Z 17.0N 124.6W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 29/0000Z...DISSIPATED $$ Forecaster Cangialosi

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