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Tropical Storm Iota Forecast Discussion Number 6

2020-11-14 22:11:05| National Hurricane Center (Atlantic)

Issued at 400 PM EST Sat Nov 14 2020 000 WTNT41 KNHC 142110 CCA TCDAT1 Tropical Storm Iota Discussion Number 6...Corrected NWS National Hurricane Center Miami FL AL312020 400 PM EST Sat Nov 14 2020 Corrected the numbering of the Key Messages and a typo in first paragraph Deep convection has re-developed closer to the low-level center of Iota during the afternoon, and there has been an increase in banding over the southeastern portion of the circulation. Data from an Air Force Reserve reconnaissance aircraft that has flown an unusually long mission from its base in Biloxi, Mississippi, indicate that the increase in organization has resulted in strengthening. The plane measured peak 925-mb flight-level winds of 55 kt, and SFMR winds of 46 kt. Those were the basis for the increase in wind speed on the 1800 UTC intermediate advisory. Given the continued increase in organization, the initial intensity has been set at 50 kt for this advisory. The aircraft reported that the minimum pressure had fallen to around 995 mb during its final pass through the center. The aircraft data indicate that Iota has not developed a tight inner core yet, but with the increase in convection closer to the center, and with the storm moving away from the coast of northwestern Colombia, it is likely Iota will begin to strengthen at a faster rate by Sunday. The upper-level wind pattern is forecast to become quite favorable while the storm traverses SSTs of around 29C. These conditions are likely to result in steady to rapid strengthening over the next couple of days and the NHC intensity forecast again predicts that Iota will be at or near major hurricane strength when it nears the coast of Central America. The SHIPS model is explicitly forecasting rapid intensification (a 30-kt increase in wind speed) over each of the next 24 h periods, and the NHC intensity forecast is quite similar, and is also in good agreement with the HFIP corrected consensus aid. Satellite imagery and the aircraft fixes show that Iota has continued to move west-southwestward today. A mid-level ridge over the Gulf of Mexico and Florida should build eastward over the western Atlantic during the next day or two. This should allow Iota to move westward to west-northwestward at a slightly faster forward speed, with this motion bringing the storm near the coast of northeastern Nicaragua or Honduras by late Monday. After landfall, a west-southwestward motion is expected to take the center of Iota inland over Central America. The track guidance has again shifted southward, partially due to the more southward initial position once again. This has resulted in another southward shift in the NHC track forecast, which is again near the TVCA multi-model consensus. The latest track forecast necessitates the issuance of a Hurricane Warning for Providencia island, and Hurricane Watches were issued earlier this afternoon for portions of the coasts of Nicaragua and Honduras. In addition to the wind and storm surge threats, Iota is likely to bring heavy rainfall and flooding to portions of Central America that are still recovering from Hurricane Eta's impacts. Key Messages: 1. Iota is expected to intensify and be at or near major hurricane strength when it approaches the coast of Central America. There is a risk of damaging wind and a dangerous storm surge across portions of Nicaragua and Honduras beginning Monday, and a Hurricane Watch is in effect for a portion of that area. 2. Hurricane conditions are expected and storm surge impacts are possible on Providencia beginning late Sunday night. Tropical storm conditions are expected and hurricane conditions are possible by Sunday evening on San Andres. 3. Through Thursday, heavy rainfall from Iota will likely lead to life-threatening flash flooding and river flooding across portions of northern Colombia and Central America. Flooding and mudslides in Honduras and Nicaragua could be exacerbated by Hurricane Etas recent effects there, resulting in significant impacts. FORECAST POSITIONS AND MAX WINDS INIT 14/2100Z 12.6N 76.5W 50 KT 60 MPH 12H 15/0600Z 12.7N 77.5W 60 KT 70 MPH 24H 15/1800Z 13.0N 78.9W 75 KT 85 MPH 36H 16/0600Z 13.4N 80.6W 90 KT 105 MPH 48H 16/1800Z 13.8N 82.2W 100 KT 115 MPH 60H 17/0600Z 14.0N 83.5W 100 KT 115 MPH...INLAND 72H 17/1800Z 14.0N 85.0W 50 KT 60 MPH...INLAND 96H 18/1800Z 13.6N 87.5W 25 KT 30 MPH...INLAND 120H 19/1800Z...DISSIPATED $$ Forecaster Brown

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Tropical Storm Theta Forecast Discussion Number 20

2020-11-14 21:38:07| National Hurricane Center (Atlantic)

Issued at 900 PM GMT Sat Nov 14 2020 890 WTNT45 KNHC 142038 TCDAT5 Tropical Storm Theta Discussion Number 20 NWS National Hurricane Center Miami FL AL302020 900 PM GMT Sat Nov 14 2020 A persistent band of deep convection to the southeast of Theta's center continues to keep it classifiable as a tropical cyclone, with the edge of the convection at one point today reaching within 60 n mi of the center of the cyclone. Over the past couple of hours this convection has become farther displaced from Theta's center, as the system gets blasted by over 40 kt of northerly shear. Since the cyclone's appearance has changed little today, the initial intensity is being held at 35 kt based off data from an ASCAT-A overpass this morning. Very strong shear and dry air entrainment should cause the deep convection to weaken and become even farther displaced from the center tonight, with Theta anticipated to degenerate into a remnant low by 12 h. The cyclone should also weaken under this regime, and open into a trough by 72 h. The latest NHC intensity forecast is unchanged from the previous one, and is in good agreement with the intensity guidance. Theta continues moving just south of due east, but now at a slower pace of around 5 kt. A mid-level ridge located to the south of Theta is weakening, which will result in a continued slow east-southeastward motion through tonight. As Theta becomes a shallow system on Sunday, the low-level flow is forecast to become southwesterly, and this flow is expected to increase on Monday ahead of an approaching cold front. This will cause Theta to turn to the northeast by late Sunday and accelerate until it dissipates in a few days. The latest NHC track forecast is similar to the previous one and lies near the track consensus models. FORECAST POSITIONS AND MAX WINDS INIT 14/2100Z 31.7N 19.2W 35 KT 40 MPH 12H 15/0600Z 31.7N 18.3W 30 KT 35 MPH...POST-TROP/REMNT LOW 24H 15/1800Z 32.1N 17.5W 30 KT 35 MPH...POST-TROP/REMNT LOW 36H 16/0600Z 33.2N 17.0W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 16/1800Z 35.1N 16.4W 20 KT 25 MPH...POST-TROP/REMNT LOW 60H 17/0600Z 38.1N 14.7W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 17/1800Z...DISSIPATED $$ Forecaster Latto

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Tropical Storm Iota Forecast Discussion Number 5

2020-11-14 15:57:59| National Hurricane Center (Atlantic)

Issued at 1000 AM EST Sat Nov 14 2020 690 WTNT41 KNHC 141457 TCDAT1 Tropical Storm Iota Discussion Number 5 NWS National Hurricane Center Miami FL AL312020 1000 AM EST Sat Nov 14 2020 Recent microwave satellite imagery and early morning visible pictures show that Iota remains a sheared tropical cyclone, with the center located near the southwestern edge of the main convective mass. The initial intensity is held at 35 kt and is based on the earlier ASCAT data and recent satellite estimates. An Air Force Reserve reconnaissance aircraft is scheduled to investigate Iota early this afternoon. Somewhat surprisingly Iota has not strengthened much since yesterday, which appears to be the result of some unexpected shear and its close proximity to the northwest coast of Colombia. The global models predict that the shear will relax soon, and that the system will be in quite favorable conditions for strengthening. The NHC forecast again calls for steady to rapid strengthening in the next 12-60 h once the storm organizes enough to take advantage of the expected favorable conditions. The updated NHC intensity is similar to the previous forecast and shows Iota at or near major hurricane strength when it approaches the coast of Central America. Although the center of Iota was relocated to the south and west of the earlier estimates, the long-term initial motion estimate is 255/4 kt. The track forecast reasoning remains unchanged from the previous advisory. A mid-level ridge over the Gulf of Mexico is expected to build eastward to the north of Iota during the next day or two, and this feature should cause the cyclone to move westward to west-northwestward at a faster forward speed during the next few days. This should bring the center near the coast of northeastern Nicaragua or Honduras in 2 to 3 days. After landfall, a west-southwestward motion is expected with Iota moving inland over Central America. The new NHC track forecast has been adjusted southward, especially in the first 24 to 36 hours due to the more southward initial position. The NHC track lies close to the TVCA multi-model consensus, which is between the lastest global model interpolated trackers and the model fields. Key Messages: 1. Iota is expected to strengthen and be at or near major hurricane strength when it approaches the coast of Central America. There is a risk of dangerous wind, storm surge, and rainfall impacts across portions of Nicaragua and Honduras beginning Monday. Hurricane Watches will likely be issued for a portion of this area later today. Tropical Storm Warnings are in effect for the islands of San Andres and Providencia. 2. Through Thursday, heavy rainfall from Iota will likely lead to life-threatening flash flooding and river flooding across portions of northern Colombia and Central America. Flooding and mudslides in Honduras and Nicaragua could be exacerbated by Hurricane Etas recent effects there, resulting in significant impacts. FORECAST POSITIONS AND MAX WINDS INIT 14/1500Z 12.7N 76.2W 35 KT 40 MPH 12H 15/0000Z 12.9N 76.8W 45 KT 50 MPH 24H 15/1200Z 13.4N 78.2W 55 KT 65 MPH 36H 16/0000Z 13.9N 80.0W 70 KT 80 MPH 48H 16/1200Z 14.2N 81.6W 85 KT 100 MPH 60H 17/0000Z 14.4N 83.0W 95 KT 110 MPH 72H 17/1200Z 14.5N 84.3W 75 KT 85 MPH...INLAND 96H 18/1200Z 14.3N 86.7W 35 KT 40 MPH...INLAND 120H 19/1200Z 13.5N 90.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Brown

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Tropical Storm Theta Forecast Discussion Number 19

2020-11-14 15:57:29| National Hurricane Center (Atlantic)

Issued at 300 PM GMT Sat Nov 14 2020 000 WTNT45 KNHC 141457 TCDAT5 Tropical Storm Theta Discussion Number 19 NWS National Hurricane Center Miami FL AL302020 300 PM GMT Sat Nov 14 2020 Theta's center continues to be devoid of deep convection as dry air entrains into the system's circulation. The edge of the only nearby surviving convection is located about 60 n mi to the southeast of the cyclone's center due to increasing northwesterly shear. A recent ASCAT overpass showed a fair amount of wind vectors of 30-34 kt, therefore the initial intensity remains 35 kt for this advisory. The shear is expected to increase even more today, and the surrounding environment is forecast to dry out further. These factors, that should persist for at least the next few days, should prevent any new convection from developing near the center of Theta. The latest NHC forecast calls for the system to become a remnant low in 12 h and dissipate in 72 h, as the circulation gradually spins down. The storm is now moving just south of due east around 7 kt as it is steered along the northern periphery of a mid-level ridge. This ridge is forecast to weaken over the next couple of days, which will cause Theta to slow its forward motion. Early next week, increasing southerly flow ahead of an approaching cold front should pick up the remnants of Theta and accelerate them northward, and then northeastward. The latest NHC track forecast is similar to the previous one and lies near the track consensus models. FORECAST POSITIONS AND MAX WINDS INIT 14/1500Z 31.8N 20.2W 35 KT 40 MPH 12H 15/0000Z 31.6N 19.1W 35 KT 40 MPH...POST-TROP/REMNT LOW 24H 15/1200Z 31.7N 18.3W 30 KT 35 MPH...POST-TROP/REMNT LOW 36H 16/0000Z 32.4N 17.8W 25 KT 30 MPH...POST-TROP/REMNT LOW 48H 16/1200Z 33.7N 17.4W 20 KT 25 MPH...POST-TROP/REMNT LOW 60H 17/0000Z 36.1N 16.4W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 17/1200Z...DISSIPATED $$ Forecaster Latto

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Tropical Storm Iota Forecast Discussion Number 4

2020-11-14 09:39:28| National Hurricane Center (Atlantic)

Issued at 400 AM EST Sat Nov 14 2020 000 WTNT41 KNHC 140839 TCDAT1 Tropical Storm Iota Discussion Number 4 NWS National Hurricane Center Miami FL AL312020 400 AM EST Sat Nov 14 2020 Satellite imagery and scatterometer data received since the last advisory indicate that Iota is a bit disorganized. The deep convection is currently not concentrated near the center, and the scatterometer wind data showed an elongated circulation with a trough extending west-southwestward from the center. The scatterometer data also showed maximum winds of 30-35 kt in the northeastern quadrant, and based on this, the initial intensity is held at 35 kt. An Air Force Reserve Hurricane Hunter aircraft is scheduled to investigate Iota at around 18Z. Iota continues to move south of west with the initial motion of 245/4 kt. A mid-level ridge over the Gulf of Mexico should build eastward to the north of Iota during the next day or two, and this feature should cause the cyclone to move westward at a somewhat faster forward speed through 72 h. This motion is expected to bring the center near or over the coasts of Nicaragua or Honduras near the 72-h point. After that time, a west-southwestward motion is forecast, with the center of the cyclone moving across portions of Central America. The new forecast track is similar to, but slightly slower than, the previous forecast, and it lies in the center of the guidance envelope near the various consensus models. Iota is currently experiencing light westerly wind shear produced by an upper-level trough to the west. The shear should subside over the next 12-24 h as the trough moves westward and dissipates, leaving the cyclone in more favorable upper-level winds and over sea surface temperatures near 29C. Thus, conditions appear conducive for steady to rapid intensification once the storm becomes well enough organized internally to take advantage of the favorable environment. The new intensity forecast is similar to the previous one, and calls for rapid intensification to major hurricane intensity, with a peak intensity of near 105 kt as the system makes landfall in Central America. It should be noted that the HWRF and HMON forecast the center to go north of the official forecast track and keep it over water north of Honduras. As a result, they forecast a stronger cyclone than indciated by the official forecast. Key Messages: 1. Iota is expected to strengthen and be a major hurricane when it approaches the coast of Central America. There is a risk of dangerous wind, storm surge, and rainfall impacts across portions of Nicaragua and Honduras beginning Monday. Hurricane Watches will likely be issued for a portion of this area later today. 2. Through Wednesday, heavy rainfall from Iota will likely lead to life-threatening flash flooding and river flooding across portions of northern Colombia and Central America. Flooding and mudslides in Honduras and Nicaragua could be exacerbated by Hurricane Etas recent effects there, resulting in significant impacts. FORECAST POSITIONS AND MAX WINDS INIT 14/0900Z 13.5N 74.8W 35 KT 40 MPH 12H 14/1800Z 13.6N 75.4W 45 KT 50 MPH 24H 15/0600Z 13.9N 76.8W 55 KT 65 MPH 36H 15/1800Z 14.3N 78.6W 70 KT 80 MPH 48H 16/0600Z 14.5N 80.4W 85 KT 100 MPH 60H 16/1800Z 14.8N 82.0W 100 KT 115 MPH 72H 17/0600Z 14.9N 83.3W 105 KT 120 MPH...INLAND 96H 18/0600Z 14.5N 86.0W 50 KT 60 MPH...INLAND 120H 19/0600Z 14.0N 89.0W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Beven

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