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Tropical Storm Genevieve Forecast Discussion Number 19

2020-08-21 04:36:45| Tropical Depression LIDIA

Issued at 900 PM MDT Thu Aug 20 2020

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Tropical Depression Fourteen Forecast Discussion Number 2

2020-08-20 22:57:44| National Hurricane Center (Atlantic)

Issued at 500 PM EDT Thu Aug 20 2020 000 WTNT44 KNHC 202057 TCDAT4 Tropical Depression Fourteen Discussion Number 2 NWS National Hurricane Center Miami FL AL142020 500 PM EDT Thu Aug 20 2020 An Air Force Reserve Hurricane Hunter aircraft investigating the system found an area of lighter winds--likely where the center would be--farther south than previous estimates. The highest flight-level wind measured by the aircraft was 30 kt at an altitude of 2500 feet, and although there were some SFMR measurements over 40 kt, these looked coincident with some heavy rain rates and thus are probably not reliable. Therefore, the initial intensity remains 30 kt. Structurally, the depression has a large cloud envelope with sporadic convective cells located in loose bands. The updated initial position derived from the aircraft data indicates that the current motion is still westward, or 270/16 kt. This southward adjustment really only affected the first 36 hours or so of the forecast, with NHC's official track forecast being shifted southward during that period. This ends up taking the cyclone's center over extreme northern Nicaragua and northeastern Honduras in 12-24 hours. After 36 hours, model guidance remains in good agreement that the system should turn northwestward due to a deep-layer trough over the Gulf of Mexico. The new set of model guidance has not shifted much from the previous cycle, and the NHC track forecast is very close to the morning forecast despite the initial position adjustment, with perhaps a slight eastward shift on days 4 and 5. In general, the NHC forecast is closest to the GFS and HCCA model solutions. The depression's farther-south position makes the intensity forecast more complicated with potentially more land interaction with parts of Central America. Slight strengthening to tropical storm strength is expected before the center reaches Honduras and Nicaragua, with little change thereafter until the center re-emerges over the Gulf of Honduras. Low shear and warm sea surface temperatures should then support further intensification up until it reaches the Yucatan Peninsula. Since there is significant uncertainty in how land interaction will affect the cyclone's intensity, the forecast intensity has been flat-lined between day 2 and day 4, with the understanding that the the winds could increase or decrease from the value shown. Vertical shear is expected to increase by day 5, and some weakening is shown at that time. Key Messages: 1. Tropical Depression Fourteen is expected to strengthen over the northwestern Caribbean Sea through Saturday, and is likely to produce tropical-storm-force winds and heavy rainfall over portions of the coasts of Nicaragua and Honduras, including the Bay Islands, beginning tonight through Friday. The system could be near or at hurricane strength when it reaches the Yucatan Peninsula of Mexico late Saturday, and watches could be required for a portion of that area tonight. 2. The system is expected to move into the south-central Gulf of Mexico as a tropical storm on Sunday. Some strengthening is anticipated while it moves northwestward over the western Gulf of Mexico early next week, but it is too soon to know exactly how strong it will get or the location and magnitude of impacts it will produce along the central or northwestern Gulf Coast. Interests in that area should continue monitoring the progress of this system over the next few days. FORECAST POSITIONS AND MAX WINDS INIT 20/2100Z 14.3N 81.0W 30 KT 35 MPH 12H 21/0600Z 14.7N 83.0W 35 KT 40 MPH 24H 21/1800Z 15.6N 84.7W 35 KT 40 MPH...INLAND 36H 22/0600Z 17.0N 85.6W 45 KT 50 MPH...OVER WATER 48H 22/1800Z 18.7N 86.6W 55 KT 65 MPH 60H 23/0600Z 20.3N 87.9W 55 KT 65 MPH...INLAND 72H 23/1800Z 22.1N 89.2W 55 KT 65 MPH...OVER WATER 96H 24/1800Z 26.0N 91.5W 55 KT 65 MPH 120H 25/1800Z 28.5N 93.5W 50 KT 60 MPH $$ Forecaster Berg

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Tropical Depression Thirteen Forecast Discussion Number 4

2020-08-20 22:53:17| National Hurricane Center (Atlantic)

Issued at 500 PM AST Thu Aug 20 2020 000 WTNT43 KNHC 202053 TCDAT3 Tropical Depression Thirteen Discussion Number 4 NWS National Hurricane Center Miami FL AL132020 500 PM AST Thu Aug 20 2020 Recent late afternoon visible satellite imagery has shown evidence of a low-level swirl that is racing away from the persistent area of deep convection. It is unclear if that is the only center of circulation or a swirl rotating around the broader circulation. The initial position for this advisory is a compromise between the earlier estimated center location and the swirl seen in satellite imagery. The initial intensity has been held at 30 kt, based on the earlier ASCAT data. The initial motion estimate is a somewhat uncertain 290/18 kt. The cyclone is located south of a subtropical ridge that is forecast to build westward over the western Atlantic through early next week. This ridge should steer the system west-northwestward over the next several days, and the suite of dynamical track models continue to be agreement on this overall scenario. The lastest NHC track foreast is similar to the previous advisory and again lies between the HFIP corrected consensus and the TVCA multi-model consensus. It should be noted that since the system is still lacking in organization, there could be some center reformations that result in some shifts in the track forecast. Although the depression has changed little in strength since it formed yesterday, the overall environment ahead of the system favors gradual strengthening. The cyclone is forecast to remain over warm water and in an area of light to moderate vertical wind shear. Most of the guidance suggests a little more favorable upper-level wind pattern once the system is north of the Greater Antilles, but a track farther south would result in more land interaction, which increases the intensity forecast uncertainty. The updated NHC intensity forecast shows a slightly slower rate of strengthening over the next couple of days, but is unchanged at the latter periods. The overall confidence in both the track and intensity forecasts remain lower than normal. Key Messages: 1. Tropical storm conditions are possible across portions of the northern Leeward Islands, the Virgin Islands, and Puerto Rico Friday night and Saturday, and Tropical Storm Watches have been issued for some of these islands. Heavy rainfall is likely across this area beginning late Friday and could cause mudslides and flash and urban flooding through Sunday. 2. The details of the long-range track and intensity forecasts are more uncertain than usual since the system could move over portions of the Greater Antilles this weekend. However, this system could bring some storm surge, rainfall and wind impacts to portions of Hispaniola, Cuba, the Bahamas, and Florida this weekend and early next week. Interests there should monitor this system's progress and updates to the forecast over the next few days. FORECAST POSITIONS AND MAX WINDS INIT 20/2100Z 16.7N 53.9W 30 KT 35 MPH 12H 21/0600Z 17.5N 57.2W 30 KT 35 MPH 24H 21/1800Z 18.3N 60.5W 35 KT 40 MPH 36H 22/0600Z 19.1N 63.5W 40 KT 45 MPH 48H 22/1800Z 20.0N 66.7W 45 KT 50 MPH 60H 23/0600Z 20.9N 70.4W 50 KT 60 MPH 72H 23/1800Z 22.2N 74.1W 60 KT 70 MPH 96H 24/1800Z 25.1N 80.4W 65 KT 75 MPH 120H 25/1800Z 28.3N 84.2W 65 KT 75 MPH $$ Forecaster Brown

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Tropical Storm Genevieve Forecast Discussion Number 18

2020-08-20 22:42:51| Tropical Depression LIDIA

Issued at 300 PM MDT Thu Aug 20 2020

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Tropical Depression Fourteen Forecast Discussion Number 1

2020-08-20 16:56:38| National Hurricane Center (Atlantic)

Issued at 1100 AM EDT Thu Aug 20 2020 046 WTNT44 KNHC 201456 TCDAT4 Tropical Depression Fourteen Discussion Number 1 NWS National Hurricane Center Miami FL AL142020 1100 AM EDT Thu Aug 20 2020 Visible satellite images indicate that the area of disturbed weather moving across the central Caribbean Sea has developed a closed surface circulation, with the center embedded beneath cellular convective cells and a large cirrus canopy. Also, convection has increased in organization, and TAFB and SAB have given the system classification of T2.0/30 kt and T1.5/25 kt, respectively. Therefore, advisories are being initiated on Tropical Depression Fourteen with maximum winds of 30 kt. An expected ASCAT pass later today and an Air Force Reserve Hurricane Hunter mission scheduled for this afternoon should give us a better handle on both the depression's center location and its maximum winds. The depression continues to move westward at a pretty good clip, currently estimated to be on a heading of 280 degrees at 18 kt. This motion is being driven by the western extent of the Bermuda high, which currently noses into the northwestern Caribbean Sea. However, a deep-layer trough over the Gulf of Mexico is expected to become the main driver in the coming days, causing the cyclone to slow down and turn rather suddenly toward the west-northwest and northwest in the next 24-36 hours. A general northwestward motion should then continue until the end of the 5-day forecast period, bringing the system across the Yucatan Peninsula Saturday night and into the central and western Gulf of Mexico early next week. Most of the reliable track models are clustered close to one another, and the official NHC track forecast is therefore very close to the multi-model consensus aids, including the HCCA model. Once the depression slows down during the next 24-36 hours, environmental conditions appear ideal for strengthening. The magnitude of vertical shear is expected to be less than 10 kt for at least the next 2 days, while the system will be moving over the deep, warm waters of the northwestern Caribbean Sea, where sea surface temperatures are 29-30 degrees Celsius. Given these conditions, some of the intensity guidance actually appears more muted than I would have expected, and I have therefore elected to closely follow the SHIPS and LGEM models, which are near the upper end of the guidance envelope. It is possible that the depression could be near or at hurricane strength when it approaches the Yucatan Peninsula of Mexico in 2-3 days. Some weakening is anticipated when the center moves over land, and then re-strengthening is likely after it moves over the Gulf of Mexico. There will be an increase in shear over the Gulf in 4-5 days, and right now there is greater-than-normal uncertainty in how this will affect the cyclone's intensity at that point. For now, the official forecast on days 4 and 5 shows a flat-lined intensity, and this scenario lies a little above the ICON intensity consensus and the HCCA model solution. Key Messages: 1. Tropical Depression Fourteen is expected to strengthen over the northwestern Caribbean Sea through Saturday, and it could produce tropical-storm-force winds and heavy rainfall over portions of the coast of Honduras and the Bay Islands beginning tonight through Friday. The system could be near or at hurricane strength when it reaches the Yucatan Peninsula of Mexico late Saturday, and watches could be required for a portion of that area later today. 2. The system is expected to move into the south-central Gulf of Mexico as a tropical storm on Sunday. Some strengthening is anticipated while it moves northwestward over the western Gulf of Mexico early next week, but it is too soon to know exactly how strong it will get or the location and magnitude of impacts it will produce along the central or northwestern Gulf Coast. Interests in that area should continue monitoring the progress of this system over the next few days. FORECAST POSITIONS AND MAX WINDS INIT 20/1500Z 15.1N 79.7W 30 KT 35 MPH 12H 21/0000Z 15.5N 81.9W 35 KT 40 MPH 24H 21/1200Z 16.3N 84.2W 40 KT 45 MPH 36H 22/0000Z 17.1N 85.5W 50 KT 60 MPH 48H 22/1200Z 18.4N 86.4W 55 KT 65 MPH 60H 23/0000Z 19.9N 87.4W 60 KT 70 MPH 72H 23/1200Z 21.5N 88.9W 45 KT 50 MPH 96H 24/1200Z 25.0N 92.0W 50 KT 60 MPH 120H 25/1200Z 28.0N 94.0W 50 KT 60 MPH $$ Forecaster Berg

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